Disease Control

Virus control will be enhanced by buying certified seed. Consult seed producers to determine what the certification covers. Destroy cull piles and volunteer plants. Do not keep potatoes for seed.

NOTE:  For the products for disease control listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 22 and Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

Seed Piece Treatment (Fungi)

Potato seed treatment is one of the more overlooked portions of a whole-season disease control program. Properly suberized and properly treated seed will provide a better, more uniform stand of plants. Proper application of the appropriate material is necessary. Too much chemical may prove phytotoxic. Inadequate coverage may not totally protect the seed-piece. Dust formulations are preferable for cut seed. CAUTION: Dip treatments may spread bacteria to seed pieces which were previously not affected. NOTE: Many of these seed treatments are now formulated with Douglas fir or alder bark as a carrier. Improved healing of the cut surface has been reported with these products. Some seed treatments can be purchased combined with imidacloprid. Do not use treated seed piotatoes for feed or food purposes.

Bacillus subtilis GB03 (Companion Liquid Biological Fungicide): 1.0-2.0 fl oz/gal.

fludioxonil (Maxim Potato seedpiece protectant): 0.5 lb/100 lb seed-pieces. (REI 12h, Group 12). Apply to cover thoroughly.

maneb/mancozeb (Maneb, Penncozeb, Manzate, Dithane): rates vary depending on formulation; see Table 23 (3 dh, REI 24h, Group M3).

pentachloronitrobenzene (Terraclor): 3.33-6.66 lb/A. ( REI 12h, Group 4) Apply a 81/2 inch band in seed furrow at planting. For control of Rhizoctonia; complete coverage is needed for satisfactory control.

Trichoderma harzianum Rifai strain KRL-AG2 (RootShield WP):  0.3-3.0 oz/100 lb seed.

Early Blight (Alternaria solani)  

Crop losses can be heavy if serious defoliation occurs before or soon after flowering. Apply any of the following fungicides when plants are 4” to 6” tall. Begin applications earlier if late blight is found in your area, or if disease forecast systems recommend beginning a protection program. Repeat at five- to seven-day intervals, depending on amount of moist weather or dew. Use shorter interval under cool (60°F to 70°F) moist conditions. Incorporate diseased vines after harvest and avoid growing pepper, tomato, and potato in a continuous rotation. Allow tubers to mature fully before harvesting, avoid harvesting when the soil is wet, and prevent mechanical injury during harvest and handling. Proper fertilization and mineral balance will reduce susceptibility of plants to early blight.

azoxystrobin (Quadris): 6.0-15.5 fl oz/A. (14 dh, REI 4h, Group 11). Apply on a 7-14 day schedule. Do not make more than one application of Quadris (or other strobiulurins) before alternating with fungicides with a different mode of action.

boscalid (Endura): 2.5-4.5 oz/A (10 dh, REI 12h, Group 7). Begin applications prior to disease onset and continue on 7-14 day intervals.

chlorothalonil (Bravo Ultrex): 0.7 lb/A before vines close between rows; 0.9-1.36 lb/A after vines close between rows or when disease severity values are reached (7 dh, REI 12h, Group M5). Apply lower rates at seven to 10 day intervals and apply at five to seven day intervals when plants are growing rapidly or disease conditions are severe.

maneb/mancozeb (Maneb, Penncozeb, Manzate, Dithane): rates vary depending on the formulation. See Table 23 (3 dh, REI 24h, Group M3).

pyraclostrobin (Headline): 6-9 fl oz/A. (3 dh, REI12h, Group 11). Do not make more than one application of Headline before alternating with a fungicide with a different mode of action. Do not alternate with Quadris.

pyrimethanil (SCALA SC Fungicide): 7 fl oz/A. ( 7 dh, REI 12h, Group 9). Use only in a tank mix with another effective early blight fungicide.

Late Blight (Phytophthora infestans)

Late blight can occur from infected seed potatoes, or infected potato debris overwintered in the field. New late blight strains introduced into the region are resistant to metalaxyl. Do not leave cull pules of potatoes in the field. The fungicides used for early blight have some protective ability against Phytophthora but cannot be relied on to provide significant control. If late blight is reported within one half mile, begin applications of an appropriate fungicide . Plants with significant disease should be plowed under. Check with your local extension specialist for the availability of special exemption fungicides.

copper hydroxide (Kocide 3000): 0.5-1.75 lb/A. (0 dh, REI 24h, Group M1). Apply on a 7 to 10-day intervals. Use highest rate when disease pressure is severe. Do not apply in a spray solution having a pH less than 6.5 or tank mix with Aliette.

cyazfamid (Ranman): 1.4-2.75 fl oz/A. (7 dh, REI 12h, Group 21). Do not make more than one application before alternating with a fungicide with a different mode of action. Addition of an organosilicone surfactant may be desirable.

cymoxanil (Curzate 60 DF): 3.2 oz/A (14 dh, REI 12h, Group 27). Do not use Curzate alone. Combine with a full rate of manzate, chlorothalonil or triphenyltin hydroxide. Do not make more than seven applications per season.

dimethomorph  (Forum): 4-6 oz/A (4 dh, REI 12h, Groups 15). Must be applied in a tank mix with a fungicide with a different mode of action. Do not make more than two sequential applications before alternating to a non-Group 15 fungicide.                                                                                                                                                                                                                                                         famoxadone plus cymoxanil (Tanos): 6-8 oz/A. (14 dh, REI 12h, Groups 11 plus 27). Must be tank mixed with an appropriate contact fungicide with a different mode of action. Do not alternate or tank mix with other Group 11 fungicides.

fenamidone (Reason 500 SC): 5.5-8.2 fl oz/A. (14 dh, REI 12h, Group 11). Do not make more than one application of Reason before alternating to a fungicide with a different mode of action. Do not alternate with Quadris, Cabrio, Flint, or Headline.

mandipropamid plus difenconazole (Revus Top): 5.5-7.0 fl oz/A. (14 dh, REI 12h, Groups 40 & 3). Addition of a spreading/penetrating type of adjuvant is recommended.  Make no more than two consecutive applications before alternating with another fungicide with a different mode of action.

mancozeb plus zoxamide (Gavel 75DF): 1.5-2.0 lb/A. (3 dh, REI 48h, Group M3 plus 22). Increase the use rate according to vine development. Use maximum labeled rate at row fill.

mefenoxam plus manzate (Ridomil Gold MZ): 2.5 lb/A. (3 dh, REI 48h, Groups 4 & M3). Apply when conditions are favorable for disease and make up to three applications at 14-day intervals. The full rate of another fungicide should be applied between Ridomil Gold applications. Do not plant any crop which is not registered for use with Ridomil Gold active ingredient in treated soil for a period of 12 months.                                                                                                                                                                              potassium salts of phosphoric acid (ProPhyt, Fosphite, Phostrol): Rates vary with formulation. (REI 4h, Group 33). Do not apply to heat or moisture stressed plants. Do not apply to plants treated with copper compounds within the last 20 days.                                                                                                                                                                                                                                            
propamocarb (Previcur Flex): 0.7 to 1.2 pt/A (14 dh, REI 12h, Group 28). See label for rates and timing. Should be tank mixed with a contact fungicide.

pyraclostrobin (Headline): 6 to 12 fl oz/A. (3 dh, REI 12h, Group 11). Apply the lower rate before symptoms develop. Do not rotate with other strobilurins such as Quadris. When late blight is present, use the higher rate at a five-day interval.

Common Scab (Streptomyces)

Scab is caused by the soilborne bacterium Streptomyces scabies. The disease tends to be prevalent when soil is dry during tuber initiation, soil pH is above 5.2, and non-decomposed manure is used as fertilizer. Continuous cropping of potato will also increase the disease. When planting susceptible varieties, avoid fields with a history of scab. When scab is present, rotate out of potatoes for at least two years. Beets, carrots, radish and some weeds can also be hosts. Maintain soil at 5.0 to 5.2. Mancozeb may be useful in controlling seed-borne scab. The varieties Norchip, Norland, Pike, Salem and Superior are resistant to scab. Allengany, Andover, Atlantic, Chieftain, Elba, Genesee, Monoma, Reba and Redsen are moderately resistant. Katahdin, Kennebec and Snowden are moderately susceptible. Chippewa, Kanona, Norwis and Yukon Gold are very susceptible.

Pythium Leak

Leak can be a problem in stored potatoes, especially bruised, immature potatoes harvested in hot weather.

mefenoxam plus manzate (Ridomil Gold MZ): 2.5 lb/A (3 dh, REI 48h, Groups 4 & M3). Make the first application at flowering and another 14 days later. If the field has a history of storage rot problems, make a third application 14 days after the second. Do not plant any crop which is not registered for use with Ridomil Gold active ingredient in treated soul for a period of 12 months.

mefenoxam plus chlorothalonil (Ridomil Gold EC/Bravo WP): 2 lb/A (3 dh, REI 48h, Groups 4 & M5). Make the first application at flowering and another 14 days later. If the field has a history of storage rot problems, make a third application 14 days after the second. Do not plant any crop which is not registered for use with Ridomil Gold EC active ingredient in treated soil for a period of 12 months.

potassium salts of phosphoric acid (PrpPhyt, Phostrol, Fosphite): Rates vary with formulation

Verticillium and Fusarium Wilt

Verticillium and Fusarium are soil-borne fungi that cause vascular wilts of potato. They can be introduced into fields by contaminated seed or soil. Continual potato production tends to result in an increase in wilt disease. A combination of lesion nematodes and Verticillium results in early dying. Rotation with nonsusceptible crops such as grasses will reduce disease. Destruction of infected potato vines by tillage encourages rapid decomposition and lessens the build-up of soil inoculum. At this time, there are no varieties resistant to Fusarium Wilt. Avoid highly susceptible cultivars and start with certified, disease-free seed pieces.

Potato Leaf Roll Virus (PLRV)

Potato Leaf Roll Virus is the most serious virus disease of potatoes in New England and can result in significant yield reductions. The virus is transmitted by aphids in a persistent manner. The virus can overwinter in unharvested tubers which may develop into virus-infected volunteer plants. Plant virus-free, certified seed. Remove volunteer plants. Rogue plants with virus symptoms. When populations of aphids reach economic thresholds, treatment is warranted. Do not use any of last year’s potato harvest for seed.

Potato Virus S (PVS), Potato Virus A (PVA), Potato Virus X (PVX), Potato Virus Y (PVY Rugose Mosaic)

These viruses may occur singly or in combination. PVY, PVS and PVA are spread by aphids in a nonpersistent manner. PVX is not known to be spread by aphids but is easily spread by plant-to-plant contact, farm machinery or cultural practices. Plant virus-free certified seed. Plant early, use resistant varieties, and control aphid populations.