Control Of Potato Late Blight Research Articles

Evaluation by computer simulation of strategies to time metalaxyl applications for improved control of potato late blight

A complex and realistic computer simulation model was used to determine the type of spray scheme utilizing metalaxyl (in mixture with a protectant fungicide) that would allow a reduction in the amount of fungicide applied but still maintain suppression of potato late blight caused by Phytophthora infestans. Timing spray applications according to some weather-based decision rules improved disease suppression relative to the standard treatment when the same or a slightly reduced total amount of fungicide was applied. However, weather-dependent spray schemes did not maintain disease control equivalent to the standard schedule when the total amount of fungicide applied was reduced by amounts > 10%. Some programmes in which spray dosages and intervals were adjusted according to time in the season resulted in much better disease suppression than the standard treatment. Reduction of the dosage in each spray application resulted in better disease suppression than reduction in the number of sprays. The dosage of sprays applied late in the season can be reduced substantially (50%) without greatly affecting disease suppression. More frequent applications at a lower dosage resulted in better disease suppression than the standard treatment even though less total fungicide was applied.

Integrated control of potato late blight (Phytophthora infestans) in Switzerland: concept and first results1

A project has been undertaken in Switzerland to reduce the number of applications of fungicides to potato by a reduction of late blight incidence and disease pressure as well as by providing reliable and precise spraying recommendations against blight. We try to achieve this aim by combining different elements: (1) to delay and to impede disease progress, it is planned to promote less susceptible potato cultivars and to reduce the number of primary foci by advising seed potato growers to protect their crops more carefully; (2) the data of about 20 weather stations are utilized to test different forecasting systems; (3) these (theoretical) indications on the appearance of the disease are complemented by extensive monitoring of real late blight occurrence in the field; (4) the late blight susceptibility of all cultivars grown in Switzerland is being assessed by special trials. From the combination of all this information, spraying recommendations will be formulated according to regions and cultivars.

Changes in the distribution of phenylamide-resistant strains ofPhytophthora infestans (Mont.) de Bary in Ireland 1985–89

Phenylamide-based fungicides were reintroduced to the Irish market in 1985. Mixtures of phenylamides and mancozeb were recommended for no more than 3 sprays in potato late blight control programmes with the last systemic spray to be applied not later than 31 July. Samples of potato foliage infected withP. infestans were collected from the main potato growing areas in Ireland over a five-year period starting in 1985. Using the floating disc method, 11% of the crops sampled in 1985 were found to have phenylamide-resistant strains ofP. infestans present. The number of crops with resistant strains increased rapidly up to 1988 when 83% of the crops sampled had resistance. Factors affecting the distribution of resistance and the efficacy of a phenylamide-based spray programme are discussed.

Environmental and biological monitoring of exposure to ethylenebisdithiocarbamate fungicides and ethylenethiourea.

Exposure of workers to ethylenebisdithiocarbamates (EBDCs; maneb or mancozeb) in 29 potato farms was evaluated during the control of potato late blight. Concentrations of EBDCs and ethylenethiourea (ETU), an impurity and degradation product in EBDC formulations, in ambient air were evaluated during pesticide application. Biological monitoring of exposure to EBDCs was carried out by measuring the concentrations of ETU, a metabolite of EBDCs, in urine for 22 days after the end of the exposure. The estimated inhaled doses of ETU and EBDCs during the average four hour application period were 0.07 and 1.8 micrograms/kg, respectively. Only 1-10% of ETU on the clothes reached the skin. The creatinine corrected concentrations of ETU in urine were 0.1-2.5 micrograms/mmol creatinine 24 hours after exposure ended. The estimated half life for eliminating ETU through the kidneys was close to 100 hours. These results indicate that the measurement of ETU in urine is suitable for biological monitoring of exposure to EBDCs.

Field Control of Potato Late Blight by Synergistic Fungicidal Mixtures

The mixture of mancozeb and cymoxanil (Mancur) and mixtures of mancozeb, cymoxanil, and oxadixyl (Pulsan and Sandocur-M) were highly effective and synergistic in controlling the phenylamide-resistant isolate of the late blight fungus. The cymoxanil mixtures may be suitable for late blight control in areas of Israel where phenylamide-resistant populations of P. infestans prevail

Determination of Mancozeb in air. Occupational exposure during its use in control of potato late blight

A simple method for the determination of occupational exposure to Mancozeb (an ethylenebisdithio-carbamate) was evaluated. This method is based on filter sampling and determination of the manganese content in the samples by means of atomic absorption spectroscopy. The method shows good linearity and accuracy for determinations in the range 0.05 to 2 mg/m 3. Exposure during field application of Mancozeb in potato cultivations was studied and was found, during preparation and filling of the spraying liquid, to be 0.22 mg/m 3 on average (n=18). The highest individual eight-hour time-weighted average exposure was 0.05 mg/m 3.

Foliar Insecticide Efficacy Trial, 1986

Abstract Certified, Class B ‘Katahdin’ seed potatoes were planted on 29 Apr at Landisville, Lancaster County, PA. Plant spacing was 9 inch with 34 inch between rows. Plot size was 4 rows x 25 ft with 2 border rows and arranged in a randomized complete block design with 4 replicates. Temik 15G (1.0 lb (AI)/acre) was applied in-furrow to all treatments including the control. Starting in Jun, Dithane M-45 was applied (1.5 lb (AI)/acre) on a 5- to 7-day schedule for potato late blight control. The foliar insecticides were applied 17 Jun, 10 and 29 Jul, and 12 Aug with a tractor-mounted boom sprayer set to deliver 30 gal per acre at 22 psi. Ten stems per plot were sampled weekly as well as before and after spraying for all stages of Colorado potato beetle (CPB). A subjective damage index was implemented: 1) indicating 0-5% leaf loss, to 5) indicating > 75% leaf loss. Two rows per plot were harvested on 16 Sep and graded by size. Average maximum and minimum daily temperatures (°F) were 79.3 and 51.4 for May, 85.3 and 56.8 for Jun, 87.0 and 62.3 for Jul, and 85.8 and 49.8 for Aug, respectively. Rainfall totalled 1.45 inches for May, 3.85 inches for Jun, 9.23 inches for Jul, and 3.76 inches for Aug.

Systemic Fungicides and the Control of Oomycetes

Diseases caused by oomycetous fungi of the order Peronosporales present major problems worldwide. Important foliar diseases include late blight on potatoes, blue mold on tobacco, grape downy mildew, plus a wide range of other foliar blights and downy mildews on cereals, fruits, vegetables, and ornamentals. Soilborne Phytophthora and Pythium spp. are equally wide­ spread and are the cause of major losses on crops as diverse as soybeans (148) and avocados (33, 51). In addition, Phytophthora and Pythium spp. are responsible for many preand postharvest problems on fruits and vegetables, including late blight of potato tubers (10), brown rot of citrus (35-37, 94), and black pod of cocoa (125, 126). Less than a decade ago our means of adequately controlling many of these diseases was extremely limited. Control of potato late blight and downy mildews involved repeated applications of protectant fungicides, starting well in advance of the general appearance of the disease. The control of many soilborne pathogens was even more limited. Fumigation with methyl bromide gas, or soil drenches with nematicides, offered only limited control for some high-value annual crops. Soilborne pathogens of field and perennial tree crops were not controlled by chemical methods, because of either cost or lack of efficacy of available chemicals. However, the discovery of systemic fungicides with good activity against Oomycetes in the early 1970s continues to revolutionize our concepts of

Foliar Insecticide Efficacy Trials, 1983

Abstract Tests were conducted at the Pennsylvania State University Agricultural Research Center at Rock Springs, Centre County, PA. A randomized complete block design with 2 replications was used. Treatment plots consisted of 3 50-ft rows planted 34 inches apart. Blocks were separated by a 20-ft alleyway. Certified, Class B ‘Katahdin’ seed potatoes were planted on 25 May ’83, with a 9 inch spacing between plants. Temik 15G (0.5 lb (AI)/acre) was applied in-furrow at planting. Carbaryl was applied weekly at 0.5 lb (AI)/acre to reduce the number of GPA predators. Dithane M-25® was applied at 1.5 lb (AI)/acre on a 7 day spray schedule for potato late blight control. The foliar insecticides were applied 22, 29 Aug, and 8 Sep with a 6-foot boom sprayer equipped with 2 Teejet® D2-25 disc-core nozzles/row. Thirty gal of water per acre were applied at 60 psi; tractor speed was 3 mph. Three leaves per plant, 12 plants per treatment plot (72 total leaves/treatment) were sampled weekly from 2 Aug to 12 Sep ’83 for green peach aphids (GPA). One row/treatment plot was harvested on 6 Oct ’83 and graded for size. Rainfall in inches totaled 0.50 May, 4.96 Jun, 1.70 Jul, 2.67 Aug, 2.16 Sep. Mean monthly temp (°F) were 59.1 May, 67.2 Jun, 71.2 Jul, 69.3 Aug and 62.6 Sep.

Foliar Insecticide Efficacy Trial, 1984

Abstract Certified, Class B ‘Katahdin’ seed potatoes were planted in Hagerstown silt loam soil at the Southeastern Field Research Station at Landisville, PA, on 3 May, with a 9-inch spacing between plants. A randomized complete block design with 4 replications was used. Plots consisted of four 25-ft rows planted 34 inches apart. Temik 15 G (1.0 lb (AI)/acre) was applied in-furrow at planting for all treatments and the control. A 3.0 lb (AI)/acre Temik treatment was also included. Dithane M-45 was applied at 1.5 lb (AI)/acre on a 5-7 day schedule for potato late blight control. The foliar insecticides were applied 22 Jun and 1 Aug, and 15 Aug with a George White boom sprayer in 22 gal per acre at 66 psi. Ten stems per plot were sampled before and after sprays for all stages of CPB. Control plots were sampled weekly beginning 12 Jun. A subjective damage estimate was also assessed, 1 for little or no damage through 5 for more than 75% defoliation. One 25-ft row per plot was harvested 4 Oct and graded by size.

Foliar Insecticide Efficacy Trial, 1983

Abstract Certified, Class B ‘Katahdin’ seed potatoes were planted 10 May, with a 9-inch spacing between plants. A randomized complete block design with 4 replications was used. Plots consisted of four 25-ft rows planted at 34 inches apart Temik 15 G (1.0 lb (AI)/acre) was applied in-furrow at planting for all treatments and the control. A 3.0 lb (AI)/acre Temik treatment was also included. Starting in Jun, Dithane M-45 was applied at 1.5 lb (AI)/acre on a 5-7 day schedule for potato late blight control. The foliar insecticides were applied 28 Jun and 26 Jul, 3, 18 Aug with a George White boom sprayer in 22 gal per acre at 66 psi. Ten stems per plot were sampled before and after sprays for all stages of CPB. Control plots were sampled weekly beginning 13 Jun. A subjective damage estimate was also assessed, 1 for little or no damage through 5 for more than 75% defoliation. One 20 ft row per plot was harvested 18 Oct and graded by size. Rainfall totalled 2.89 inches for Jun, .28 inches for Jul and 3.27 inches for Aug. Avg max and min daily temperatues (°F) were 83.1 and 57.5 for Jun, 89.8 and 60.1 for Jul and 89.2 and 61.4 for Aug.

Resistance to acylalanines in Phytophthora infestans in The Netherlands1

In The Netherlands in 1980 a severe late‐blight epidemic involving metalaxyl‐resistant strains of Phytophthora infestans did considerable damage to the potato crop. As a consequence metalaxyl or metalaxyl‐containing products were withdrawn from the Dutch fungicide market for the control of potato late blight. In 1981 the majority of the P. infestans isolates obtained from various parts of the country were sensitive to metalaxyl. In three areas where metalaxyl mixtures were used on a relatively large scale metalaxyl‐resistant strains dominated the population. Incidental use of metalaxyl mixtures in 1982 and 1983 showed adequate late‐blight control and, when in 1984 an early and in some areas severe epidemic developed, a metalaxyl/mancozeb mixture was reintroduced for curative application in combination with conventional fungicides. Although disease control was adequate, resistant strains were present in a small number of fields. Whether resistant strains will increase in frequency and threaten the usefulness of mixtures of acylalanines will heavily depend on how well potato farmers adopt strategies involving a limited use of mixtures of acylalanines in a spray schedule with conventional late‐blight fungicides.

Synthetic Pyrethroid Insecticide Efficacy Trial, 1982

Abstract Certified, Class B ‘Norchip’ seed potatoes were planted 6 May with a 9-in spacing between plants. A randomized complete block design with four replications was used. Plots consisted of four 20-ft rows planted 34 in apart. Temik 15G (1.0 lb (AI)/acre) was applied in-furrow at planting for all treatments and the control. A 3.0 lb (AI)/acre Temik treatment was also included. Starting 8 Jun., Dithane M-45 was applied at 1.5 lb (AI)/acre on a 5 to 7 day schedule for potato late blight control. The foliar insecticides were applied 6 and 27 Jul., with a Myers air blast sprayer in 50 gal. of water per acre at 200 lb/in2. Forty stems per plot were sampled each week for all stages of Colorado potato beetle (CPB) beginning 25 Jun. A subjective damage estimate was also assessed. Two rows per plot were harvested 30 Aug. and graded by size. Rainfall totalled 8.36 in for June, 2.74 in for Jul. and 1.10 in for Aug. Average maximum and minimum daily temperatures (°F) were 78.2 and 56.7 for Jun., 86.0 and 62.3 for Jul., and 82.5 and 56.2 for Aug.

Impact of Foliar Sprays on Green Peach Aphids and Ladybird Beetles, 1982

Abstract Certified, Class B ‘Katahdin’ seed potatoes were planted on 4 May, with a 9-inch spacing between plants. A randomized complete block design with three replications was used. Treatment plots consisted of three 25-ft rows planted 34 inches apart. A 10-ft alleyway separated blocks. Temik 15 G (2.0 lb (AI)/acre) was applied in furrow at planting. Dithane M-45 was applied at 1.5 lb (AI)/acre on a 7-day schedule for potato late blight control. The foliar insecticides were applied 30 Jul., 13 Aug., 23 Aug., and 13 Sep. in 40 gal of water per acre at 62 lb/in2 with a 6-ft boom sprayer equipped with three TeeJet D2-25 disc-core cone nozzles per row. Tractor speed was 3 mph. Three leaves per plant, three plants per treatment plot (27 total leaves/treatment) were sampled weekly from 12 Jul. to 16 Sep. for green peach aphids. The number of ladybird beetle predators was counted on one stem per plant, three stems per treatment plot (nine total stems/treatment). A minimum of one row per treatment was harvested from each block on 5 Oct. and graded for size. Rainfall in inches totaled 3.07 May, 7.71 Jun., 4.11 Jul., 1.72 Aug., 2.80 Sep. Mean monthly temperatures (°F) were 61.5 May, 63.5 Jun., 71.1 Jul., 65.4 Aug., and 61.2 Sep.

Efficacy of Temik, 1982

Abstract Temik 15G applied at planting and post planting, was evaluated on a Hagerstown silt loam at the Southeastern Field Research Station at Landisville, Lancaster, Pa. A randomized complete block design with four replicates was used. Plots consisted of eight 20-ft rows planted 34 in apart. Certified Class B ‘Katahdin’ seed potatoes were planted 6 May, 1982, with a 9-in spacing between plants. Dithane M-45 was applied at 1.5 lb (AI)/acre on a 7-day schedule for potato late blight control. Three application techniques were evaluated: Temik applied once in-furrow at planting, as a split application in furrow followed by a side dress application on 25 Jun, and as a single layby application after plants had emerged on 16 Jun. Light cultivations preceeded and followed the layby and side dress applications. Forty stems were sampled each week for all stages of the Colorado potato beetle from 21 Jun until 19 Jul. A subjective damage estimate was also assessed. Two rows per plot were harvested 16 Sep, 1982 and graded by size. Rainfall totalled 8.36 inches in Jun, 2.74 inches in Jul, 1.10 inches in Aug and 3.17 inches in Sep. Average maximum and minimum temperatures (°F) were 78.2 and 56.7 for Jun, 86.0 and 62.3 for Jul, and 82.5 and 56.2 for Aug, and 77.1 and 51.7 for Sep.

Control of Green Peach Aphid with Foliar Sprays, 1983

Abstract Certified, Class B ‘Katahdin’ seed potatoes were planted on 25 May, with a 9-inch spacing between plants. A randomized complete block design with two replications was used. Treatment plots consisted of three 50-ft rows planted 34 inches apart. Blocks were separated by a 20-ft alleyway. Temik 15 G (0.5 lb (AI)/acre) was applied in furrow at planting. Carbaryl was applied weekly at 0.5 lb (AI)/acre to reduce the number of green peach aphid predators. Dithane M-45 was applied at 1.5 lb (AI)/acre on a 7-day spray schedule for potato late blight control. The foliar insecticides were applied 22 Aug., 29 Aug., and 8 Sep. in 30 gal of water per acre at 60 lb/in2 with a CO2-pressurized tractor-mounted boom sprayer equipped with two TeeJet D2-25 disc-core cone nozzles/row. Tractor speed was 3 mph. Three leaves per plant, 12 plants per treatment plot (72 total leaves/treatment) were sampled weekly from 2 Aug. to 12 Sep. for green peach aphids (GPA). One row/treatment plot was harvested on 6 Oct. and graded for size. Rainfall in inches totaled 0.50 May, 4.96 Jun., 1.70 Jul., 2.67 Aug., 2.16 Sep. Mean monthly temperatures (°F) were 59.1 May, 67.2 Jun., 71.2 Jul., 69.3 Aug. and 62.6 Sep.

Potato late blight control and top desiccation when pesticides are applied with a controlled droplet and a conventional sprayer

Disease development was observed in field plots to which two different fungicides, each at two rates, were applied regularly with either a conventional or a controlled droplet sprayer. The type of fungicide did not affect disease severity, but more disease damage occurred in the controlled droplet sprayer plots than in conventional sprayer plots. Reduced rates of fungicide resulted in higher disease incidence ratings than recommended rates of fungicides by end of the spraying season. Lower marketable tuber yields and greater incidences of late blight tuber rot were related to foliar disease levels, the different sprayer types, and rates of applied fungicide. No significant differences in terms of potato top desiccation efficacy between the two sprayer types were obtained. In addition, total tuber yield and level of vascular discoloration were similar for both the controlled droplet and conventional sprayer.

Synthetic Pyrethroid Insecticide Efficacy Trial, 1979

Abstract A randomized complete block design with 3 replications was used at the Southeastern Field Research Laboratory in Lancaster County, PA. Plots consisted of four 20 ft rows, each plot separated by a 5 ft alleyway. Row spacing was 34 inches and seed tubers were set 9 inches apart within rows. Certified, Class B ‘Katahdin’ seed tubers were planted Jun 7. Temi k 15G was applied in furrow at planting at 3.0 lb ai/acre. Dithane M-45 was applied at 1.5 lb ai/acre on a 5-7 day schedule for potato late blight control. The foliar insecticides were applied on Aug 9 and Sep 7 with a Meyers air blast sprayer in 50 gal of water per acre at 200 psi. Ten stems per plot were sampled weekly for all stages of Colorado potato beetle (CPB) beginning on Jul 3. Green peach aphid (MyzuspersicaeSulz.) populations were limited by an early season application of Pirimor 50WP. Two rows per plot were harvested on Oct 2b and graded by size. Precipitation totalled 2.67 inches in Jun, 5.43 inches in Jul, 3.39 inches in Aug, and 5.96 inches in Sep. Average maximum and minimum temperatures (0F) were 79.0 and 55.5 for Jun, 83.2 and 60.8 for Jul, 82.5 and 60.7 for Aug and 76.9 and 52.5 for Sep. Approximately 1.71 inches of rain fell within 3 days after the Aug 9 application which may have reduced efficacy. CPB severity was light to moderate. Insecticide application was delayed until an acceptable infestation had developed in the plots.

Efficacy of Temik, 1979

Abstract A randomized complete block design with 4 replications was used at the Southeastern Field Research Laboratory in Lancaster County, PA. Plots consisted of eight 40 ft rows planted 34 inches apart, separated by a 5 ft alleyway. Certified, Class B ‘Katahdin’ seed potatoes were planted Jun 7 at a 9 inch spacing between plants. Four rates of Temik were applied with an electric, tractor-mounted Gandy granular applicator. Ten stems per plot were sampled each week for all stages of Colorado potato beetle beginning on Jul 3. Pirimor 50WP was applied as a foliar spray early in the season for green peach aphid (Myzus persicae Sulz.) control. Dithane M-45 at 1.5 lb ai/acre was applied on a 5-7 day schedule for potato late blight control. Two rows per plot were harvested Oct 26 and graded by size. The test was conducted on a Hagerstown silt loam soil. Rainfall totalled 2.67 inches in Jun, 5.43 inches in Jul, 3.39 inches in Aug, and 5.96 inches in Sep.

Synthetic Pyrethroid Insecticide Efficacy Trial, 1980

Abstract At the Southeastern Field Research Laboratory, Lancaster County, PA a randomized complete block design with 4 replications was used. Plots consisted of four 24 ft rows planted 34 inches apart. Certified, Class B ‘Norchip’ seed potatoes were planted on May 8, with a 9 inch spacing between plants. Two rows of corn were planted along each plot to reduce drift. Temik 15 G (3.0 lb ai/acre) was applied in furrow at planting. Dithane M-45 was applied at 1.5 lb ai/acre on a 5-7 day schedule for potato late blight control. Pirimor 50 WP was applied early in the season to eliminate green peach aphid (Myzus persicaeSulz.) populations. The foliar insecticides were applied Jul 3, 21, Aug 13, and 28 with a Myers air blast sprayer in 50 gal of water per acre at 200 psi. Ten stems per plot were sampled each wk for all stages of Colorado potato beetle (CPB) beginning Jun 29. A subjective damage estimate was also assessed, 1 for little or no damage through, 5 for more than 75% defoliation. Two rows per plot were harvested Sep 22 and graded by size. Rainfall totalled 5.03 inches for Jun, 3.65 inches for Jul, and 2.64 inches for Aug. Maximum and minimum average daily temperatures (0F) were 80.5 and 53.5 for Jun, 87.8 and 61.9 for Jul and 87.8 and 62.5 for Aug. Approximately 0.74 inches of rain followed the Jul 21 application, and temperatures were above 85 F on this date and Aug 25 which may have effected efficacy of these compounds.