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Selective control of Orobanche ramosa in potato with rimsulfuron and sub-lethal doses of glyphosate
ARTICLE IN PRESS
Crop Protection 24 (2005) 743–747 www.elsevier.com/locate/cropro
Selective control of Orobanche ramosa in potato with rimsulfuron and sub-lethal doses of glyphosate M.A. Haidar, M.M. Sidahmed, R. Darwish, A. Lafta Faculty of Agricultural and Food Sciences, American University of Beirut, Riad El-Solh, Beirut 1107 2020, Lebanon Received 25 October 2004; received in revised form 15 December 2004; accepted 6 January 2005
Abstract Previous studies indicated that foliar applications of rimsulfuron were effective in controlling Orobanche ramosa but phytotoxic to potato plants, while sub-lethal doses of glyphosate slightly reduced Orobanche infestation but were selective in potato. In this study, a single foliar application of rimsulfuron at 12.5 g ai/ha followed by single and sequential foliar applications [20, 35, 50 days after potato emergence (DAPE)] of sub-lethal doses of glyphosate (100, 200 and 300 g ai/ha) were used. All doses except the single application of rimsulfuron followed by sequential applications of glyphosate at 200 and 300 g ai/ha had no negative effect on potato growth and marketable yield, but had variable effects on Orobanche infestation. All doses significantly reduced Orobanche shoot number 75 and 90 DAPE, while triple application of glyphosate following rimsulfuron was the most effective in reducing Orobanche shoot number after 110 DAPE and dry weight compared to the control. The best results considering both Orobanche control and selectivity in potato was obtained by application of rimsulfuron at 12.5 g ai/ha followed by sequential foliar application (three times) of glyphosate at 100 g ai/ha. r 2005 Elsevier Ltd. All rights reserved. Keywords: Potato; Orobanche; Rimsulfuron; Glyphosate
1. Introduction Orobanche ramosa Forsk (Branched broomrape) is an annual root holoparasitic higher plant in the family Orobanchaceae. It parasitizes roots of various agronomic and vegetable broad leaved crops (Parker and Riches, 1993) and some weeds like Lamium amplexicaule (Haidar, personal observation) Malva nicaeansis and Rhagadiolus stellatus (Abu-Irmaileh, personal communication). In Lebanon, this species parasitizes mainly solanaceae crops such as potato and tomato. Severe reduction in potato yield quantity and quality were observed with high levels of Orobanche field infestations (Haidar and Bibi, 1995). As most traditional strategies aimed at controlling Orobanche infestation in the field have limited effect, the search for new methods Corresponding author. Tel.: +961 1 350000; fax: +961 1 744460.
E-mail address: [email protected] (M.A. Haidar). 0261-2194/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2005.01.005
for controlling Orobanche has become increasingly important. One of the most promising methods for controlling Orobanche is the use of sub-lethal doses of glyphosate on crops that show tolerance to glyphosate (Elzein and Kroschel, 2003; Parker and Riches, 1993; Jacobsohn and Levy, 1986). The idea is to apply low doses of glyphosate to the host leaves, so that it moves through the host phloem to underground Orobanche attachment on the host roots and exert its toxic effect, thus inhibiting Orobanche growth prior to its shoot emergence. Low doses of glyphosate were found to be effective against Orobanche spp. in broad bean (Kasasian, 1973; Schmitt et al., 1979), sunflower (CastejonMunoz et al., 1990), tomato (Kotoula-Syka and Eleftherohorinos, 1990), carrot and celery (Elzein and Kroschel, 2003), and vetch (Nandula et al., 1999). However, the use of this herbicide, to our knowledge, has not been tested or confirmed in potato, most likely
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because of its limited selectivity, time and rate of application. Previous field studies showed that sequential application of rimsulfuron was effective in controlling O. ramosa but injured potato plants (Haidar et al., 2005). Preliminary greenhouse studies showed that sequential application of sub-lethal doses of glyphosate (three times) at 100 g ai/ha was selective in potato but slightly reduced Orobanche infestation (unpublished data). This suggested the use of sequential application of both herbicides with few modifications. Accordingly, studies were initiated to examine Orobanche ramosa control with a single foliar application of rimsulfuron followed by a single or sequential application of sub-lethal doses of glyphosate in potato.
2. Materials and methods 2.1. General experimental procedures Experiments were conducted in a naturally infested field with Orobanche ramosa at the Agricultural Research and Education Center (AREC) of the American University of Beirut, Lebanon in the spring of 2004. The soil is silty clay loam with a pH of 7.6, 2.35% organic matter and EC of 0.26 ms/cm. All plots were tilled twice with a mouldboard, disked and levelled 1 week prior to planting. The experimental area received a uniform application of 2.9 t/ha of NPK (17:17:17) during planting. Nitrogen (ammonium nitrate, 33.5%) was applied in bands 35 days after planting at a rate of 300 kg/ha. Plots were sprinkler irrigated every 6 days. The standard potato cultivar ‘‘Spunta’’ was planted on April 23, 2004. Certified potato seeds (tuber pieces) were planted at 3.0 t/ha. Plots (5 m long and 2.25 m wide) were hilled 35 days after planting (standard practice by Lebanese farmers). Potato rows were 0.70 m apart and within-the-row spacing was around 0.30 m. To eliminate all weeds other than Orobanche, the entire experimental area received a standard soil application of metribuzin (SencorR 70%) at 0.65 kg ai/ ha 1 week after sowing. The whole experimental area received a single foliar application of rimsulfuron (Technical grade, 75% DF, from Dupont) at 12.5 g ai/ha. A single foliar application of rimsulfuron at 12.5 g ai/ha was applied 20 days after potato emergence (DAPE) followed by a sequential application of foliar sub-lethal doses of glyphosate (Round upR, 48%) at 100, 200 and 300 g ai/ha applied at 20, 35 and 55 DAPE. The above doses were chosen after a preliminary greenhouse study. All herbicides were applied with a CO2-pressurized backpack sprayer that delivered 375 L/ha at 138 kPa through a Teejet 8002 flat fan spray tips. Irrigation water was withheld for 2 days after each spraying. Potato plants were 20–25 cm
tall at 20 DAPE. No surfactant was added to the spray solution. 2.2. Experimental measurements and statistical analyses Experimental plots (three rows per plot) were arranged in a factorial randomized complete block design with five replications. Factors evaluated were glyphosate sub-lethal doses and application timing (20, 35 and 50 DAPE). All data were subjected to analysis of variance and Fishers tests. Protected Least Significant Difference (LSD) Test at p ¼ 0:05 level of probability was used to determine significant differences between treatments means. Orobanche data included shoot number (70, 90 and 110 DAPE) which had emerged from the soil, and shoot dry weight per m2 of the middle row. Potato data included number of plants per row, phytotoxicity visual rating, height/five plants, leaves, stems and total fresh weight of three plants of the right row (90 DAPE), total and marketable yield. Potato yield was determined by harvesting the middle row (3.5 m2) in each plot. Yield quality was determined by separating harvested tubers into two classes: marketable (46 cm diameter) and nonmarketable tubers (o5 cm in diameter).
3. Results and discussion 3.1. Orobanche management A single application of rimsulfuron alone or followed by a single or sequential application of sub-lethal doses of glyphosate at 100 or 200 g ai/ha significantly reduced Orobanche shoot number after 75 and 90 DAPE as compared to the control (Table 1). Glyphosate at 300 g ai/ha was extremely toxic to potato plant after first application and therefore was discontinued. All treatments reduced Orobanche infestation by 100% after 75 DAPE. Rimsulfuron followed by sequential application of sub-lethal doses of glyphosate (three times) at all doses were the most effective treatments in reducing Orobanche shoot number after 110 DAPE and shoot dry weight. This treatment reduced Orobanche infestation by 77% when glyphosate was applied at 100 g ai/ha and 90% when applied at 200 g ai/ha. Low doses of systemic herbicides as split or sequential applications have been found very effective against Orobanche in various crops. Split application with low doses of sulfunylurea herbicides inhibited Orobanche growth in potato (Goldwasser et al., 2001) and tomato (Hershenhorn et al., 1998). Sequential application of sub-lethal doses of glyphosate has also been found effective against Orobanche in many crops (Elzein and Kroschel, 2003). The significance of using split or sequential application of systemic herbicides on the
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Table 1 Effects of glyphosate and rimsulfuron on Orobanche shoot number and dry weight per m2 Treatment dose (g ai/ha)
Application time (DAPE)
Shoot number DAPE 75
Glyphosate
100 200 100 200 100 200
Rimsulfuron Control
Shoot dry wt. (g)
90
20 20 20/35 20/35 20/35/50 20/35/50
0.0 0.0 0.0 0.0 0.0 0.0
b b b b b b
20
0.5 b 11 a
110
6.0 0.0 3.0 2.3 0.0 0.0
bc c bc bc c c
38.0 27.0 43.0 21.0 15.0 6.0
13 b 32 a
abc abc abc bc c c
21.0 15.0 17.0 5.0 5.0 5.0
60.5 ab 65.0 a
ab ab ab b b b
36.0 a 36.0 a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
Table 2 Response of potato growth to glyphosate and rimsulfuron 90 DAPE Treatment dose (g ai/ha)
Application time (DAPE)
Plant no. per row
Phytotoxicity visual rating (%)
Plant ht. (cm)
Glyphosate
20 20 20/35 20/35 20/35/50 20/35/50
12.0 12.0 12.0 12.0 11.0 11.0
8.0 7.0 7.0 6.0 7.0 5.0
76.0 64.0 64.0 47.0 63.0 51.0
20
12.0 a 12.0 a
100 200 100 200 100 200
Rimsulfuron Control
a a a a a a
ab bcd abc cd ad d
8.0 ab 8.0 ab
abc be be e be de
85.0 a 81.0 ab
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test. Scale (0–10), with 0 indicating complete death and 10 no injury.
Table 3 Effect of glyphosate and rimsulfuron on potato biomass 90 DAPE Treatment dose (g ai/ha)
Glyphosate
Rimsulfuron Control
100 200 100 200 100 200
Application time (DAPE)
Average fresh weight of three plants/plot (n ¼ 5) (g/plant) Leaves
Stems
Total shoot
20 20 20/35 20/35 20/35/50 20/35/50
183.0 133.0 127.0 67.0 109.0 69.0
50.0 30.0 32.0 27.0 30.0 29.0
233.0 163.0 159.0 94.0 139.0 98.0
20
141.0 ab 126.0 ab
ab ab ab b ab b
a a a a a a
54.0 a 34.0 a
a abc abc c bc c
196.0 ab 160.0 abc
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
host during the growing season is to inhibit Orobanche growth prior to shoot emergence. Orobanche seeds are continuously induced to germinate by potato roots and develop the attachment organ, the germ tube or radicle. Sequential application of systemic herbicides may prevent the attachment of the organ or its differentiation and allow for early season control of Orobanche.
3.2. Potato biomass and yield Results in Table 2 show that rimsulfuron alone or followed by a sequential application of sub-lethal doses of glyphosate at all doses had no significant effect on potato plant number. However, sequential application of glyphosate at 200 g ai/ha following rimsulfuron
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Table 4 Yield response of potato to glyphosate and rimsulfuron Treatment dose (g ai/ha)
Glyphosate
Rimsulfuron Control *
100 200 100 200 100 200
Application time (DAPE)
Total yield (t/ha)
Tuber distribution (% of total yield) Tuber diameter (cm) 5
6.4–7.4
7.5
Marketable yield (t/ha)
20 20 20/35 20/35 20/35/50 20/35/50
31.3 29.6 27.6 28.0 33.3 28.3
a a a a a a
23 35 27 32 21 30
61 53 53 51 57 52
16 12 20 17 22 19
24.0 19.7 20.3 19.0 26.3 19.2
ab ab ab b a b
20
32.0 a 27.3 a
15 22
39 52
47 26
27.3 a 21.3 ab
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
application was toxic to potato plants and significantly reduced potato shoot height. Visual potato injury appeared 10 days after first spraying and included leaf yellowing, plant stunting and compact potato plants, compared to the control (Table 2). All treatments had no effect on leaves, stems and total fresh weight of potato shoots 90 DAPE (Table 3). Rimsulfuron alone and/or followed by sequential application of glyphosate had no significant effect on total potato yield (Table 4). Sequential application (three times) of glyphosate at 100 g ai/ha following rimsulfuron, was selective in potato and had no negative effect on tuber quality. However, sequential application of rimsulfuron and glyphosate at 200 g ai/ha was the most toxic treatment and produced non-marketable potato tubers. Phytotoxicity was mostly reflected in the tuber quality of potato yield grown for fresh market with a high incidence of deformed and small tubers (Fig. 1). The number of deformed tubers increased with repeated application of glyphosate at 200 g ai/ha. Even though potato tubers under this treatment were small and deformed, there was a significant difference in total yield compared to the control from the increase in the number of non-marketable tubers. Many researchers reported the destructive effect of low doses of imidazolinone and glyphosate on various crops. Potato (Haidar et al., 2005) and tomato (Kotoula-Syka and Eleftherohorinos, 1990) were sensitive to imidazolinone, while pea (Arjona-Berral et al., 1984), sunflower (Castejon-Munoz et al., 1990) and tomato (Kotoula-Syka and Eleftherohorinos, 1990) were sensitive to glyphosate. Thus, selectivity remains the main obstacle in host plants and is mediated by the time and dose of application of systemic herbicides (Elzein and Kroschel, 2003; MesaGarcia and Garcia-Torres, 1985). These results suggest that single foliar application of rimsulfuron at 12.5 g ai/ha followed by three foliar applications of glyphosate at 100 g ai/ha could
Fig. 1. Deformed potato tubers with cracks or fissures caused by a single application of rimsulfuron followed by a sequential application of glyphosate at 200 g ai/ha.
be used selectively to control Orobanche ramosa in potato.
Acknowledgments The authors wish to express their appreciation to Inaam El-Rassy and Rana El-Hajj for their technical assistance.
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References Arjona-Berral, A., Vazouez-Cobo, A., Garcia-Torres, L., 1984. Broomrape (Orobanche crenata Forsk) control in lentils (Lens esculenta L.) and peas (Pisum sativum L.) with glyphosate and propyzamide. Proceedings of the Third EWRS Symposium on Weed Problems in the Mediterranean Area, Deiras, Portugal, pp. 293–298. Castejon-Munoz, M., Romero-Munoz, F., Garcia Torres, L., 1990. Control of broomrape (Orobanche cernua Loelf) in sunflower (Helianthus annus L.) with glyphosate. Crop Prot. 9, 332–336. Elzein, A., Kroschel, J., 2003. Progress on management of parasitic weeds. In: Labrada, R. (Ed.), Weed Management for Developing Countries. Plant Production and Protection Paper 120, Add. 1,. FAO, Rome, pp. 109–143. Goldwasser, Y., Eizenberg, H., Hershenhorn, J., Plakhine, D., Blumenfeld, T., Buxbaum, H., Golan, S., Kleifeld, Y., 2001. Control of Orobanche aegyptiaca and O. ramosa in potato. Crop Prot. 20, 403–410. Haidar, M.A., Iskandarani, N., Sidahmed, M., Darwish, R., 2005. Susceptibility of Orobanche ramosa and potato tolerance to rimsulfuron. Crop Protection 24, 7–13. Haidar, M.A., Bibi, W., 1995. Common weeds of Lebanon. Arab and Near East Plant Protection Newsletter, Abstract, 34. Beirut, Lebanon.
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Hershenhorn, J., Plakhine, D., Goldwasser, Y., Westwood, J.H., Foy, C.L., Kleifeld, Y., 1998. Effect of sulfonylurea herbicides on early development of Egyptian broomrape (Orobanche aegyptiaca) in tomato (Lycopersicon esculentum). Weed Technol. 12, 108–114. Jacobsohn, R., Levy, D., 1986. Glyphosate for Orobanche control in various crops: problems and promises. In: ter Borg, S.J. (Ed.), Proceedings, Workshop on Biology and Control of Orobanche. Wageningen, The Netherlands, pp. 172–175. Kasasian, L., 1973. Control of Orobanche. PANS 19, 368–371. Kotoula-Syka, E., Eleftherohorinos, I.G., 1990. Orobanche ramosa L. (broomrape) control in tomatoes (Lycopersicon esculentum Mill) with chlorosulfuron, glyphosate and imazaquin. Weed Res. 31, 19–27. Mesa-Garcia, J., Garcia-Torres, L., 1985. Orobanche crenata Forsk. Control in Vicia faba L. With glyphosate as affected by herbicide rates and parasite growth stages. Weed Res. 25, 129–134. Nandula, V.K., Foy, C.L., Orcutt, D.M., 1999. Glyphosate for Orobanche aegyptiaca control in Vicia sativa and Brassica napus. Weed Sci. 47, 486–491. Parker, C., Riches, C.R., 1993. Parasitic Weeds of the World: Biology and Control. Cab International, Wallingford, UK 332pp. Schmitt, U., Schulter, K., Boorsma, P.A., 1979. Control quimico de Orobanche crenata en habas. Boletin Fitosanitario FAO, vol. 29, pp. 88–91.
Crop Protection 24 (2005) 743–747 www.elsevier.com/locate/cropro
Selective control of Orobanche ramosa in potato with rimsulfuron and sub-lethal doses of glyphosate M.A. Haidar, M.M. Sidahmed, R. Darwish, A. Lafta Faculty of Agricultural and Food Sciences, American University of Beirut, Riad El-Solh, Beirut 1107 2020, Lebanon Received 25 October 2004; received in revised form 15 December 2004; accepted 6 January 2005
Abstract Previous studies indicated that foliar applications of rimsulfuron were effective in controlling Orobanche ramosa but phytotoxic to potato plants, while sub-lethal doses of glyphosate slightly reduced Orobanche infestation but were selective in potato. In this study, a single foliar application of rimsulfuron at 12.5 g ai/ha followed by single and sequential foliar applications [20, 35, 50 days after potato emergence (DAPE)] of sub-lethal doses of glyphosate (100, 200 and 300 g ai/ha) were used. All doses except the single application of rimsulfuron followed by sequential applications of glyphosate at 200 and 300 g ai/ha had no negative effect on potato growth and marketable yield, but had variable effects on Orobanche infestation. All doses significantly reduced Orobanche shoot number 75 and 90 DAPE, while triple application of glyphosate following rimsulfuron was the most effective in reducing Orobanche shoot number after 110 DAPE and dry weight compared to the control. The best results considering both Orobanche control and selectivity in potato was obtained by application of rimsulfuron at 12.5 g ai/ha followed by sequential foliar application (three times) of glyphosate at 100 g ai/ha. r 2005 Elsevier Ltd. All rights reserved. Keywords: Potato; Orobanche; Rimsulfuron; Glyphosate
1. Introduction Orobanche ramosa Forsk (Branched broomrape) is an annual root holoparasitic higher plant in the family Orobanchaceae. It parasitizes roots of various agronomic and vegetable broad leaved crops (Parker and Riches, 1993) and some weeds like Lamium amplexicaule (Haidar, personal observation) Malva nicaeansis and Rhagadiolus stellatus (Abu-Irmaileh, personal communication). In Lebanon, this species parasitizes mainly solanaceae crops such as potato and tomato. Severe reduction in potato yield quantity and quality were observed with high levels of Orobanche field infestations (Haidar and Bibi, 1995). As most traditional strategies aimed at controlling Orobanche infestation in the field have limited effect, the search for new methods Corresponding author. Tel.: +961 1 350000; fax: +961 1 744460.
E-mail address: [email protected] (M.A. Haidar). 0261-2194/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2005.01.005
for controlling Orobanche has become increasingly important. One of the most promising methods for controlling Orobanche is the use of sub-lethal doses of glyphosate on crops that show tolerance to glyphosate (Elzein and Kroschel, 2003; Parker and Riches, 1993; Jacobsohn and Levy, 1986). The idea is to apply low doses of glyphosate to the host leaves, so that it moves through the host phloem to underground Orobanche attachment on the host roots and exert its toxic effect, thus inhibiting Orobanche growth prior to its shoot emergence. Low doses of glyphosate were found to be effective against Orobanche spp. in broad bean (Kasasian, 1973; Schmitt et al., 1979), sunflower (CastejonMunoz et al., 1990), tomato (Kotoula-Syka and Eleftherohorinos, 1990), carrot and celery (Elzein and Kroschel, 2003), and vetch (Nandula et al., 1999). However, the use of this herbicide, to our knowledge, has not been tested or confirmed in potato, most likely
ARTICLE IN PRESS 744
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because of its limited selectivity, time and rate of application. Previous field studies showed that sequential application of rimsulfuron was effective in controlling O. ramosa but injured potato plants (Haidar et al., 2005). Preliminary greenhouse studies showed that sequential application of sub-lethal doses of glyphosate (three times) at 100 g ai/ha was selective in potato but slightly reduced Orobanche infestation (unpublished data). This suggested the use of sequential application of both herbicides with few modifications. Accordingly, studies were initiated to examine Orobanche ramosa control with a single foliar application of rimsulfuron followed by a single or sequential application of sub-lethal doses of glyphosate in potato.
2. Materials and methods 2.1. General experimental procedures Experiments were conducted in a naturally infested field with Orobanche ramosa at the Agricultural Research and Education Center (AREC) of the American University of Beirut, Lebanon in the spring of 2004. The soil is silty clay loam with a pH of 7.6, 2.35% organic matter and EC of 0.26 ms/cm. All plots were tilled twice with a mouldboard, disked and levelled 1 week prior to planting. The experimental area received a uniform application of 2.9 t/ha of NPK (17:17:17) during planting. Nitrogen (ammonium nitrate, 33.5%) was applied in bands 35 days after planting at a rate of 300 kg/ha. Plots were sprinkler irrigated every 6 days. The standard potato cultivar ‘‘Spunta’’ was planted on April 23, 2004. Certified potato seeds (tuber pieces) were planted at 3.0 t/ha. Plots (5 m long and 2.25 m wide) were hilled 35 days after planting (standard practice by Lebanese farmers). Potato rows were 0.70 m apart and within-the-row spacing was around 0.30 m. To eliminate all weeds other than Orobanche, the entire experimental area received a standard soil application of metribuzin (SencorR 70%) at 0.65 kg ai/ ha 1 week after sowing. The whole experimental area received a single foliar application of rimsulfuron (Technical grade, 75% DF, from Dupont) at 12.5 g ai/ha. A single foliar application of rimsulfuron at 12.5 g ai/ha was applied 20 days after potato emergence (DAPE) followed by a sequential application of foliar sub-lethal doses of glyphosate (Round upR, 48%) at 100, 200 and 300 g ai/ha applied at 20, 35 and 55 DAPE. The above doses were chosen after a preliminary greenhouse study. All herbicides were applied with a CO2-pressurized backpack sprayer that delivered 375 L/ha at 138 kPa through a Teejet 8002 flat fan spray tips. Irrigation water was withheld for 2 days after each spraying. Potato plants were 20–25 cm
tall at 20 DAPE. No surfactant was added to the spray solution. 2.2. Experimental measurements and statistical analyses Experimental plots (three rows per plot) were arranged in a factorial randomized complete block design with five replications. Factors evaluated were glyphosate sub-lethal doses and application timing (20, 35 and 50 DAPE). All data were subjected to analysis of variance and Fishers tests. Protected Least Significant Difference (LSD) Test at p ¼ 0:05 level of probability was used to determine significant differences between treatments means. Orobanche data included shoot number (70, 90 and 110 DAPE) which had emerged from the soil, and shoot dry weight per m2 of the middle row. Potato data included number of plants per row, phytotoxicity visual rating, height/five plants, leaves, stems and total fresh weight of three plants of the right row (90 DAPE), total and marketable yield. Potato yield was determined by harvesting the middle row (3.5 m2) in each plot. Yield quality was determined by separating harvested tubers into two classes: marketable (46 cm diameter) and nonmarketable tubers (o5 cm in diameter).
3. Results and discussion 3.1. Orobanche management A single application of rimsulfuron alone or followed by a single or sequential application of sub-lethal doses of glyphosate at 100 or 200 g ai/ha significantly reduced Orobanche shoot number after 75 and 90 DAPE as compared to the control (Table 1). Glyphosate at 300 g ai/ha was extremely toxic to potato plant after first application and therefore was discontinued. All treatments reduced Orobanche infestation by 100% after 75 DAPE. Rimsulfuron followed by sequential application of sub-lethal doses of glyphosate (three times) at all doses were the most effective treatments in reducing Orobanche shoot number after 110 DAPE and shoot dry weight. This treatment reduced Orobanche infestation by 77% when glyphosate was applied at 100 g ai/ha and 90% when applied at 200 g ai/ha. Low doses of systemic herbicides as split or sequential applications have been found very effective against Orobanche in various crops. Split application with low doses of sulfunylurea herbicides inhibited Orobanche growth in potato (Goldwasser et al., 2001) and tomato (Hershenhorn et al., 1998). Sequential application of sub-lethal doses of glyphosate has also been found effective against Orobanche in many crops (Elzein and Kroschel, 2003). The significance of using split or sequential application of systemic herbicides on the
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Table 1 Effects of glyphosate and rimsulfuron on Orobanche shoot number and dry weight per m2 Treatment dose (g ai/ha)
Application time (DAPE)
Shoot number DAPE 75
Glyphosate
100 200 100 200 100 200
Rimsulfuron Control
Shoot dry wt. (g)
90
20 20 20/35 20/35 20/35/50 20/35/50
0.0 0.0 0.0 0.0 0.0 0.0
b b b b b b
20
0.5 b 11 a
110
6.0 0.0 3.0 2.3 0.0 0.0
bc c bc bc c c
38.0 27.0 43.0 21.0 15.0 6.0
13 b 32 a
abc abc abc bc c c
21.0 15.0 17.0 5.0 5.0 5.0
60.5 ab 65.0 a
ab ab ab b b b
36.0 a 36.0 a
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
Table 2 Response of potato growth to glyphosate and rimsulfuron 90 DAPE Treatment dose (g ai/ha)
Application time (DAPE)
Plant no. per row
Phytotoxicity visual rating (%)
Plant ht. (cm)
Glyphosate
20 20 20/35 20/35 20/35/50 20/35/50
12.0 12.0 12.0 12.0 11.0 11.0
8.0 7.0 7.0 6.0 7.0 5.0
76.0 64.0 64.0 47.0 63.0 51.0
20
12.0 a 12.0 a
100 200 100 200 100 200
Rimsulfuron Control
a a a a a a
ab bcd abc cd ad d
8.0 ab 8.0 ab
abc be be e be de
85.0 a 81.0 ab
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test. Scale (0–10), with 0 indicating complete death and 10 no injury.
Table 3 Effect of glyphosate and rimsulfuron on potato biomass 90 DAPE Treatment dose (g ai/ha)
Glyphosate
Rimsulfuron Control
100 200 100 200 100 200
Application time (DAPE)
Average fresh weight of three plants/plot (n ¼ 5) (g/plant) Leaves
Stems
Total shoot
20 20 20/35 20/35 20/35/50 20/35/50
183.0 133.0 127.0 67.0 109.0 69.0
50.0 30.0 32.0 27.0 30.0 29.0
233.0 163.0 159.0 94.0 139.0 98.0
20
141.0 ab 126.0 ab
ab ab ab b ab b
a a a a a a
54.0 a 34.0 a
a abc abc c bc c
196.0 ab 160.0 abc
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
host during the growing season is to inhibit Orobanche growth prior to shoot emergence. Orobanche seeds are continuously induced to germinate by potato roots and develop the attachment organ, the germ tube or radicle. Sequential application of systemic herbicides may prevent the attachment of the organ or its differentiation and allow for early season control of Orobanche.
3.2. Potato biomass and yield Results in Table 2 show that rimsulfuron alone or followed by a sequential application of sub-lethal doses of glyphosate at all doses had no significant effect on potato plant number. However, sequential application of glyphosate at 200 g ai/ha following rimsulfuron
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Table 4 Yield response of potato to glyphosate and rimsulfuron Treatment dose (g ai/ha)
Glyphosate
Rimsulfuron Control *
100 200 100 200 100 200
Application time (DAPE)
Total yield (t/ha)
Tuber distribution (% of total yield) Tuber diameter (cm) 5
6.4–7.4
7.5
Marketable yield (t/ha)
20 20 20/35 20/35 20/35/50 20/35/50
31.3 29.6 27.6 28.0 33.3 28.3
a a a a a a
23 35 27 32 21 30
61 53 53 51 57 52
16 12 20 17 22 19
24.0 19.7 20.3 19.0 26.3 19.2
ab ab ab b a b
20
32.0 a 27.3 a
15 22
39 52
47 26
27.3 a 21.3 ab
Means followed by the same letter, within each column, do not significantly differ at the 5% level according to the LSD test.
application was toxic to potato plants and significantly reduced potato shoot height. Visual potato injury appeared 10 days after first spraying and included leaf yellowing, plant stunting and compact potato plants, compared to the control (Table 2). All treatments had no effect on leaves, stems and total fresh weight of potato shoots 90 DAPE (Table 3). Rimsulfuron alone and/or followed by sequential application of glyphosate had no significant effect on total potato yield (Table 4). Sequential application (three times) of glyphosate at 100 g ai/ha following rimsulfuron, was selective in potato and had no negative effect on tuber quality. However, sequential application of rimsulfuron and glyphosate at 200 g ai/ha was the most toxic treatment and produced non-marketable potato tubers. Phytotoxicity was mostly reflected in the tuber quality of potato yield grown for fresh market with a high incidence of deformed and small tubers (Fig. 1). The number of deformed tubers increased with repeated application of glyphosate at 200 g ai/ha. Even though potato tubers under this treatment were small and deformed, there was a significant difference in total yield compared to the control from the increase in the number of non-marketable tubers. Many researchers reported the destructive effect of low doses of imidazolinone and glyphosate on various crops. Potato (Haidar et al., 2005) and tomato (Kotoula-Syka and Eleftherohorinos, 1990) were sensitive to imidazolinone, while pea (Arjona-Berral et al., 1984), sunflower (Castejon-Munoz et al., 1990) and tomato (Kotoula-Syka and Eleftherohorinos, 1990) were sensitive to glyphosate. Thus, selectivity remains the main obstacle in host plants and is mediated by the time and dose of application of systemic herbicides (Elzein and Kroschel, 2003; MesaGarcia and Garcia-Torres, 1985). These results suggest that single foliar application of rimsulfuron at 12.5 g ai/ha followed by three foliar applications of glyphosate at 100 g ai/ha could
Fig. 1. Deformed potato tubers with cracks or fissures caused by a single application of rimsulfuron followed by a sequential application of glyphosate at 200 g ai/ha.
be used selectively to control Orobanche ramosa in potato.
Acknowledgments The authors wish to express their appreciation to Inaam El-Rassy and Rana El-Hajj for their technical assistance.
ARTICLE IN PRESS M.A. Haidar et al. / Crop Protection 24 (2005) 743–747
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