Only certified seed should be used. Diseased seed not only affects the plants that grow from it but puts the rest of the field and the whole farming operation at risk because many diseases can be spread by cutters, planters, and other equipment. In addition, diseased plants from affected seed tubers serve as the primary inoculum source from which other plants in the field can be infected as the inoculum is spread by wind, rain, and insect activity. This is the same risk posed by leaving cull piles exposed in the vicinity of production fields. A grower often cannot tell by looking at tubers whether they will be good for seed. Fortunately, the New York State Foundation Seed Certification Program can survey for these problems. Seed growers can obtain meristem-produced, disease-free plantlets or high quality seed from the Uihlein Foundation Seed Potato Farm at Lake Placid, which is administered by Cornell University. Seed producers are required to use a “flush-out” system, obtaining new seed from the state seed farm each year and producing a limited number of generations. Seed more than four or five generations old often poses a higher production risk for commercial use because repeated field exposure increases the probability of disease introduction and spread within a seed lot which may significantly reduce yields and pose a serious risk of other problems.

When handling seed, growers should maintain lot identity and prevent contamination. Trucks, storage, and handling equipment must be clean and disinfected between each lot of certified seed. Placing seed in storages that have been treated with chlorpropham (CIPC) may result in delayed or irregular sprouting, poor stand, and low yield.

Seed tubers should be stored at 40°F and high humidity to prevent premature sprouting and dehydration. Tubers should be warmed to 50° to 60°F before being handled and cut. Curing cut seed is best accomplished by placing seed in half-full pallet boxes or spread out in piles only a few feet deep with adequate air circulation, temperature between 55° and 60°F, and about 90 percent relative humidity. After cut seed has been held at optimal curing conditions for one week, the storage temperature should be lowered to between 40° and 45°F to maintain vigor and avoid excessive sprout growth.

For most varieties grown in New York State, seed weight of

1.5 to 2 ounces is optimal. Cut seed should be blocky in shape to reduce the cross-sectional area and facilitate uniform planting by equipment. Mechanical seed cutters should be adjusted to seed size and shape, and seed should be graded to a uniform size before cutting. See Table 23.2.1.

Chemical treatment is not a substitute for disease-free seed or good sanitation and handling, but it can reduce losses from disease when cut seed is held before planting or is planted into cold, wet soil. It can also prevent the introduction into noninfested soils of surface-borne organisms that cause diseases such as scab, Rhizoctonia, Verticillium wilt, and blackleg.

23.3 Fertility

Soils should be tested frequently for nutrient levels and pH. Many fields with a long history of potato production have accumulated large amounts of phosphorus and potassium (potash). Excessive levels of potash can depress specific gravity. Low soil pH reduces the availability of phosphorus and increases the availability of toxic elements such as iron and aluminum. To control common scab, soil pH should be kept within a relatively narrow range (5.0 to 5.2). If scab-resistant varieties are used, potatoes can be grown in soil with pH levels near 6.0, increasing the availability of phosphorus and other soil nutrients.

All lime and fertilizer recommendations should be based on soil test history. Mineral soils should have pH determined in calcium chloride and should have measurements made of

iron, aluminum, and manganese in addition to the traditional measurements of phosphorus (P), potassium (K), and magnesium (Mg). See Table 23.3.1 for the recommended application rates of nitrogen, phosphorus, and potassium. If soil magnesium is below 100, apply 50 pounds of MgO per acre (30 lb magnesium per acre).

23.4 Harvesting

23.4.1 Enhancing Color of Red Skinned Varieties

To enhance skin color of red skinned varieties, apply 2.3 oz of Riverdale 2,4-D L.V. 4 Ester at bud stage. An additiional application ten days later is allowable. The color of smooth skinned varieties such as Chieftan is intensified by one or two applications. Color enhancement does not occur when 2,4-D is applied to clones with slightly netted skin.

23.4.2.2 Vine Killing

Chemical vine killing is used to aid in the harvest operation by desiccating potato vines and weeds and conditioning tubers to reduce bruising and skinning during harvest and handling. It also controls tuber size, minimizes incidence of

hollow heart, and helps control diseases such as late blight

and leafroll. Ideally, chemical vine kill should simulate natural plant death. Rapid plant death can cause vascular discoloration, and in severe cases, the tissue at the stem of the tuber can become sunken and discolored. This affects the outward appearance of the tuber and provides an entry for decay causing organisms. High rates of chemicals, dry soils,

Table 23.2.1 Potato seed (cwt) required to plant one acre
	34” between rows				36” between rows
Distance between	Weight of seed pieces (oz)				Weight of seed pieces (oz)
seed in row	1	1.5	1.75	2	1	1.5	1.75	2
inches	cwt
6	19	29	34	38	18	27	32	37
8	14	22	25	29	14	20	24	27
10	11	17	20	23	11	16	19	22
12	10	14	17	19	9	14	16	18
15	8	11	14	16	7	11	13	14

Table 23.3.1 Recommended application rate of nutrients based on soil tests.
N pounds/acre	P₂O₅ pounds/acre			K₂O pounds/acre				Comments
	Soil Phosphorus Level			Soil Potassium Level
	low	med.	high	low	med.	high	very high
120-175	240	180	120	240	120	75	50	Mineral soils only

75-125	100	75	50	100	75	50	50	Muck soils only

1: Apply 75-100 lb N/A in bands at planting, then apply remainder when plants are 4-8 inches tall. Reduce N rate by 75 lb/A if a good stand of clover or alfalfa is plowed down. Adjust N rate to suit variety grown (see section 24.1)

2: If pH levels are below 5.2 or iron plus aluminum levels are above 200, apply 240 lb phosphate/A regardless of soil phosphate level. Banded phosphate is more available than broadcast applications.

Table 23.4.1 Vine killing chemicals and application rates
Compound(s)
Common name		Rate/A	PHI	REI	Field
	Trade name	Product	(days)	(hours)	Use EIQ	Comments
endothall
	Desicate II 2 lb/gal	1.5 -2 qt	10	48	41-65	Use 1.5-2 quarts in 5-30 gallons of spray per acre for aerial or ground applications. The addition of 4 to 5 lb/A of ammonium sulfate and a surtactant may improve effectiveness. Use the higher rate of Desicate II 2L for vigorous vines or during cool, cloudy conditions.
paraquat + nonionic adjuvant (X-77)
	*Gramoxone Max	.7-1.3 pts.	3	Varies (see label)	7-12	FOR FRESH MARKET POTATOES ONLY. Do not use to desiccate vines of seed or storage potatoes grown on muck soils. Do not apply to drought stressed plants or to vigorously growing vines
*Restricted use only.

Table 23.4.2 Disinfectants.
Compound(s)
Common name
	Trade name	Rate	Comments
sodium hypochlorite
	5.25% chlorine bleach (Clorox, Lysol, etc.)	1 gal/10 gal water	For use on machinery and floors.

and warm temperatures encourage rapid vine kill. Use low rates of chemicals on hot, dry days and higher rates in cool weather. Do not allow vine killers to drift onto neighboring foliage or crops. Under good conditions, the time between vine killing and harvest is ten to 14 days. For specific chemicals and application rates, see Table 23.4.1

23.4.3 Facility Sanitation

Facilities and handling equipment such as bin pilers should be cleaned and disinfected properly before potatoes are placed in storage. See Table 23.4.2. Bins or equipment treated with quaternary ammonium compounds must be rinsed with drinkable water before coming into contact with potatoes intended for human consumption. Structural, mechanical, and electrical problems should be identified and repaired before the storage area is filled. Check for breaks in moisture barriers and insulation to avoid cold spots during the winter.

23.4.4 Curing and Storage

Cuts and bruises heal most rapidly under conditions described previously for precutting seed. High relative humidity at 50° to 60°F should be provided for two to three weeks at the beginning of the storage period. After this, the temperature should be gradually lowered to 40°F for tablestock or seed or maintained at 50°F for chipstock varieties such as Atlantic or Norchip or at 45°F for Kanona, Monona, or Snowden. When a condition such as field frost, late blight, or ring rot that favors decay is present, the curing period should be eliminated and the temperature dropped as soon as possible.

Desired storage temperature is best achieved with forced-air ventilation controlled thermostatically by an air proportioning system. Air flow should be uniform throughout the storage facility to maintain consistent temperature and oxygen levels. Air flow rates early in the storage season may range from a continuous flow of 1/2 to 1 cu. ft./cwt/min. with high relative humidity to enhance the curing process. Later a maintenance program should use an air flow of 1/2 to 4/5 cu. ft./cwt/min. as needed (five to ten percent of the time). If severe rot potential exists, continous air flow rates as high as two cu. ft./cwt/min. may be required to cool and dry the tubers. Excessive air flow rates, particularly at low relative humidity, will dehydrate tubers and interfere with the wound healing process. Relative humidity in storage should be as high as possible without causing condensation on the tubers and the storage structure. Good insulation properly protected with a vapor barrier reduces the danger of condensation.

23.4.5 Sprout Inhibitors

Sprout inhibitors should be used in conjunction with good storage management. Although most potato varieties are dormant for two to three months after harvest, they will eventually sprout even in low temperature cold storage. Two chemical sprout inhibitors are available to lengthen the storage period. Maleic hydrazide is applied as a field spray on green foliage two to three weeks after the full bloom stage. This material is translocated to the tubers and helps prevent sprouting. Chlorpropham (CIPC) is applied as an aerosol through the air ventilation system of the storage facility or as a spray on tubers on the packing line. For specific application rates, see Table 23.4.3. Because the normal warning signal of sprouting will have been suppressed, it is important to examine tubers in the center and at the base of the pile at frequent intervals during the storage season to make sure that storage rots, internal sprouting, or other disorders are not developing. Seed potatoes should not be treated with either material or stored.

Table 23.4.3 Sprout inhibitors
Compound(s)
Common name		Rate/A	PHI	REI	Field
	Trade name	Product	(days)	(hours)	Use EIQ	Comments
maleic hydrazide
	Drexel Sprout Stop Royal MH-30	1-1.33 gal/30-150 gal water 2 gal/30 gal water		12 12	47 47	Apply to growing plants when the smallest tubers are 1.5” in diameter, except for Norchip, which must be at least 2” in diameter. Vines must remain green at least several weeks after application. Allow at least a 2 week interval before use of a vine killer. Do not use on seed potatoes.
chlorpropham (CIPC)
	Sprout Nip	—	—	—	—	Apply directly to tubers. Use as a commercially applied aerosol treatment in storage or as an emulsifiable concentrate applied as a spray after washing tubers. Apply after cuts and bruises have healed (2-3 weeks after harvest). Under dosage may increase internal sprouting. Seed potatoes may show delayed sprouting if placed in treated storage, even if all treated potatoes are removed first. Federal law requires that shipping containers are labeled with the chemical name of this inhibitor.

Table 23.4.4 Nonpathogenic disorders.
Disorder	Management Option	Recommendation
Air pollution	Variety selection	Andover and Norland are particularly sensitive varieties.
Hollow heart	Variety selection. Maintain uniform growing conditions	Varieties differ in severity. Avoid growing oversized tubers. Utilize appropriate plant spacing. Irrigate and fertilize for specific variety requirements.
Internal necrosis	Variety selection. Minimize heat stress	Varieties differ in susceptibility. Irrigation reduces soil temperatures and increases calcium uptake.
Blackspot	Avoid bruising tubers Maintain tuber turgor	Minimize impact events during harvesting, transporting, grading, and handling. Store in high humidity and warm before handling operations.
Secondary tubers	Avoid old seed	Purchase good quality seed and keep in cold storage.

23.5 Disease Management

23.5.1 Seed piece decay and seedborne pathogens primarily caused by Fusarium dry rot, Rhizoctonia black scurf, Helminthosporium silver scurf, common scab, and bacterial soft rot pathogens

Time for concern: Plant emergence

Key characteristics:

*Management Option*		*Recommendation*
Resistant varieties		No resistant varieties are available.
Site selection		Seed planted into warm, well-drained soil will emerge faster.
Seed selection/treatment		Seed quality is the most important factor in minimizing losses due to this disease. Plant only certified seed. Carefully inspect seed at the time of receipt. If possible, evaluate the seed before it is shipped. For a guide to potato seed evaluation see Reference 1. Seed treatment is the second most important consideration to optimize stand establishment and early-season growth. Seed should be warmed to 50°F before handling, cutting, or planting.
Planting		Shallow planting and light cultivation to break up compact soil will increase soil temperature, improve oxygen levels around the seed piece, and speed plant growth.
Note(s)		Physiological disorders due to lack of oxygen and cold temperatures during storage or transit contribute to seed piece problems and poor stand establishment.
Scouting/thresholds, Crop rotation, Postharvest, and Sanitation		These are not currently viable management options.
Compound(s)
Common name	Rate/A		PHI	REI	Field
Trade name	Product		(days)	(hours)	Use EIQ	Comments
Seed Piece Treatments
fludioxonil + mancozeb
Maxim MZ	0.5 lb/cwt		—	24	1-2	Use Maxim MZ (Groups 12 + M3) against Rhizoctonia black scurf, silver scurf, black dot, Fusarium and seed piece late blight. Also labeled for use for seed potato production.
flutolanil + mancozeb
Moncoat MZ	0.75-1 lb/cwt		—	24	<1	Use Moncoat MZ (Groups 7 + M3) against Rhizoctonia, Fusarium dry rot and seed piece late blight.
mancozeb
Potato Seed Treater PS	1 lb/cwt		—	24	—	Use mancozeb (Group M3) for Fusarium seed piece decay, for seed piece LB movement, common scab, Rhizoctonia stem canker, and silver scurf.
Dithane 75 DF Manzate Penncozeb	1.25 lb/50 gal		—	24	—
maneb + streptomycin
Seed Treatment for Potatoes	1 lb/cwt		—	24	—	Suppression of Fusarium dry rot, Rhizoctonia, and black leg.
imidacloprid + mancozeb
Gaucho-MZ	0.75 lb/cwt		—	24	—	Suppression of Fusarium dry rot, Rhizoctonia, and seed piece late blight. Aids in control of aphids, Colorado potato beetle and other insects.

Compound(s)
Common name	Rate/A	PHI	REI	Field
Trade name	Product	(days)	(hours)	Use EIQ	Comments
Seed Piece Treatments
imidacloprid + thiophanate-methyl + mancozeb
Tops-MZ-Gaucho	0.75 lb/cwt	—	24	—	Tops-MZ-Gaucho (fungicide Groups 1 + M3) has activity towards Rhizoctonia, silver scurf, Fusarium dry rot and seed piece late blight. Aids in control of aphids, Colorado potato beetle, and other insects.
thiophanate-methyl + mancozeb + cymoxanil
Evolve	0.75 lb/cwt	—	24	—	Evolve (Fungicide Groups 1 + M3 + 27) has activity towards Rhizoctonia, silver scurf, Fusarium dry rot and better activity towards seed piece late blight.
thiophanate-methyl + mancozeb
Tops MZ	0.75 lb/cwt	—	24	—	Tops MZ (Fungicide Groups 1 + M3) has activity towards Rhizoctonia, silver scurf, Fusarium dry rot and seed piece late blight.
Trichoderma harzianum
T-22 Planter Box	0.5-2 oz/cwt	—	0	—	For suppression of Rhizoctonia black scurf and stem canker. Not effective in cool and wet soils.
In-Furrow Treatments
azoxystrobin
Quadris F	In-furrow 0.4-0.8 fl oz/1000 row feet	—	4	<1	Quadris and Amistar (Group 11) are effective for control of Rhizoctonia, silver scurf and black dot. Use higher rate if field location is conductive for disease development or if potatoes are grown on muck soils.
Amistar 80WDG	0.125-0.25 oz/ 1000 row feet	—	4	<1
flutolanil
† Moncut 70DF	0.71-1.1 lb/A	—	12	12-19	Not for use in Nassau/Suffolk Counties. May leak into ground water. Moncut (Group 7) is used for control of Rhizoctonia stem canker and black scurf.
pentachloronitrobenzene (PCNB)
Blocker 4F	5-10 pts (5.2-10.4 fl oz/ 1000 row feet)	—	12	146-291	For Rhizoctonia control, apply in 10-20 gallons of water per acre based on a 34-inch row spacing. Spray an 8.5 inch band into seed furrow at time of planting.
Terraclor F	5-10 pts (5.2-10.4 fl oz/ 1000 row feet)
† Not for use in Nassau/Suffolk Counties

23.5.2 Bacterial soft rot, Erwinia spp.

Time for concern: Between harvesting and marketing

Key characteristics: Bacteria may be present in lenticels, which appear as tan or water-soaked areas on the tuber surface. Advanced infections will be seen as soft rot of the tuber flesh. The amount of damage depends on the population of the bacteria on and in the seed, seed storage and handling practices, and variety susceptibility. See Reference 1.

*Management Option*			*Recommendation*
Resistant varieties			No resistant varieties are available.
Site selection			Infection of the lenticels is common in saturated soils.
Seed selection/treatment			Plant disease-free seed.
Harvest			Avoid injuries to the tuber during harvest.
Note(s)			Soft rot bacteria infects through the stolons or through lesions created by other disease organisms or wounds.
Postharvest			The use of chlorine wash treatments can prevent the spread of decaying bacteria by killing the organism on contact. See Section 10.1 in the Postharvest Handling chapter. Provide good conditions for wound healing (55° to 60°F and 95 percent relative humidity, with good ventilation) for two to three weeks. Following the curing period, temperatures should be kept as low as possible. Do not move potatoes unnecessarily during the storage period because new wounds will be created. Severely affected tuber lots should not be stored.
Scouting/thresholds, Crop rotation, and Sanitation			These are not currently viable management options.
Compound(s)
Compound(s) Common name		Rate/A		Comments
	Trade name	Product
Sodium hypochlorite
	AgClor 310	65-125 ppm		Add to wash water. The temperature of the water and the potato should be close. Follow label directions. Water pH should be between 6 and 7.5.

23.5.3 Fusarium dry rot primarily Fusarium sambucinum and Fusarium solani

Time for concern: Planting, harvest, and postharvest

Key characteristics: Symptoms include sunken and shriveled areas on the surface of the tubers. The rot may extend to the center of the tuber and contain a fungal growth that is pink, white, or yellow. Affected tissue often becomes colonized by soft rot bacteria. See References 1 and 2.

*Management Option*			*Recommendation*
Scouting/thresholds			Inspect seed for Fusarium dry rot before purchasing. If necessary, grade out affected tubers before cutting seed.
Note(s)			The Fusarium dry rot pathogens have developed resistance to thiophanate-methyl.
Resistant varieties			No resistant varieties are available.
Site selection			Plant seed with a Fusarium problem in warm ground and cover with as little soil as practical.
Seed selection/treatment			Purchase seed with as little dry rot as possible. Seed becomes more susceptible as the storage season progresses. Warm seed to at least 50°F before handling and cutting to minimize injury and promote growth. Bruising the seed during handling spreads the disease. Treat seed with a fungicide. Protect seed from wind and sunlight during planting because dehydration weakens seed. Cut only as much seed as can be planted within 24 hours. Cut with sharp knives and disinfect seed cutting and handling equipment often. Always disinfect between seed lots. Do not mix seed lots.
*Management Option*			*Recommendation*
Harvest			Harvest tubers after skins are set and when pulp temperature is greater than 50°F.
Postharvest			The fungus infects through wounds at harvest. Avoid injuries to the tuber and provide conditions for wound healing in storage (55° to 60°F and 95 percent relative humidity with good ventilation) for two to three weeks. Following the curing period, temperatures should be kept as low as possible. Do not move potatoes unnecessarily during storage because new wounds will spread the disease.
Crop rotation and Sanitation			These are not currently viable management options.
Compound(s)
Common name		Rate/A		PHI	REI	Field
	Trade name	Product		(days)	(hours)	Use EIQ	Comments
thiabendazole
	Mertect 340-F 3.8 lb/gal	0.42 fl oz/2000 pounds		—	12	<1	Apply Mertect (Group 1) uniformly in a fine mist with water to each ton of potatoes as tubers pass over a bin loader. Do not apply to cut tubers. Note: Fusarium resistance makes disease control unpredictable.

23.5.4 Early blight, Alternaria solani, A. tomatophila

Time for concern: Early to mid-July through harvest

Key characteristics: Leaf lesions are dark brown and appear leathery with faint, concentric rings giving a “target-spot” effect. Spots grow to 1/2 inch. Tuber infections appear as small, irregular, brownish black spots which are usually sunken. The rotted tuber tissue is firm, hard, and somewhat corky. Tuber infection is much less common than foliar infection. See References 1, 3, and 4.

*Management Option*			*Recommendation*
Scouting/thresholds			Record the occurrence and severity of early blight. No thresholds have been established.
Resistant varieties			Potato varieties differ in their susceptibility to early blight. Onaway is particularly susceptible.
Note(s)			Environmental stress such as drought increases plant susceptibility.
Crop rotation			Minimum two year rotation without potatoes, tomatoes, or eggplants if severe outbreaks have occurred.
Seed selection/treatment			Plant disease-free, certified seed.
Vine killing			Infection to tubers can be reduced by allowing tubers to mature in the ground for at least two weeks after the vines die. Dig when the vines are dry.
Harvest			Avoid wounding during harvest.
Sanitation			Plow under all plant debris and volunteer potatoes immediately after harvest.
Site selection and Postharvest			These are not currently viable management options.
Compound(s)
Common name		Rate/A		PHI	REI	Field
	Trade name	Product		(days)	(hours)	Use EIQ	Comments
azoxystrobin
	Quadris F	6.2-15.4 fl oz		14	4	1-3	Do not apply more than 1 sequential foliar application of these products or other strobilurin (Group 11) before alternating with a fungicide that has a different mode of action. Do not spray these three products where spray drift may reach apple trees or use same sprayer to apply sprays to apple trees.
	Amistar 80 WDG	2-5 oz		14	4	2-4
azoxystrobin + chlorothalonil
	Quadris Opti	1.6 pt		14	12	42

Compound(s)
Common name		Rate/A	PHI	REI	Field
	Trade name	Product	(days)	(hours)	Use EIQ	Comments
boscalid
	Endura 70 WDG	2.5-4.5 oz	30	12	5-7	Do not make more than two sequential applications Boscalid (Group 7) before alternating to a labeled fungicide with a different mode of action.
chlorothalonil
	Bravo, Equus or OLF 6 lb/gal	0.75-1.5 pt	7	12	16-33	Note eye wash requirement and reduced seasonal amounts for shortened reentry interval on label.
famoxadone + cymoxanil
	Tanos 50 DF	6 oz	14	12	1	See comments below.
Do not make more than one application of Tanos (Groups 11 + 27) before alternating to an effective fungicide with a different mode of action (other than Group 11). Tanos must be tank-mixed with an appropriate contact fungicide that has a different mode of action (eg. chlorothalonil [M5] or mancozeb [M3]), using at least the minimum labeled rate of each fungicide. Also labeled for the control of Brown Spot (Alternaria alternata). For best results in controlling Brown Spot, tank-mix Tanos with a mancozeb or maneb fungicide
fenamidone
	*† Reason 500 SC	5.5-8.2 fl oz	14	12	3-5	†Not for use or sale in Nassau or Suffolk Counties. See comments below.
For optimum results, begin applications of Reason (Group 11) when environmental conditions become favorable for disease development. Do not make more than 1 application before alternating with a fungicide with good efficacy for control of Early Blight and the other diseases on the label. Alternating fungicide should have a different mode of action (other than Group 11).
iprodione
	Rovral 50 WP 0.5 lb/lb	1-2 lb	14	24	6-11	Rovral belongs to fungicide Group 2.
mancozeb
	Dithane 75DF or OLF 0.75 lb/lb	1-2 lb	3	24	11-22	Apply up to 4 applications. For alternation and as tank-mix protectant.
maneb
	Maneb 75DF 0.75 lb/lb	1.5-2 lb	3	24	24-32	For alternation and as tank-mix protectant.
	Manex 4 lb/gal	1.2-1.6 qt	3	24	19-25	For alternation and as tank-mix protectant.
metiram
	Polyram 80 DF 0.8 lb/lb	1.5-2 lb	3	24	48-64	For alternation and as tank-mix protectant.
pyraclostrobin
	Headline EC	6-9 fl oz	3	12		Do not make more than one application of Headline (Group 11) before alternating to a labeled fungicide with a different mode of action. No aerial application in NYS.
pyrimethanil
	Scala SC + protectant	7 fl oz	7	12	3	Use Scala (Group 9) only in a tank mix with the recommended dose rate of another effective early blight fungicide.
triphenyltin hydroxide + maneb
	*Super Tin 80 WP or OLF +	1.87 oz	7	48	9	In addition to controlling blight, use of Super Tin or OLF (Group 30) may suppress Colorado potato beetle feeding and reduce egg laying and larval survival. Note new maximum allowable amounts per season. Higer rates of Super Tin or OLF (2.5-3.75 oz) are used when not combined with another fungicide registered for potato disease control.
	Maneb 75 DF or OLF	8-16 oz			8-16

Compound(s)
Common name		Rate/A	PHI	REI	Field
	Trade name	Product	(days)	(hours)	Use EIQ	Comments
zoxamide + mancozeb
	*Gavel 75DF	1.5-2 lb	3	48	30-40	Begin application of Gavel (Groups 22 + M3) at first sign of disease.
*Restricted use only		† Not for use in Nassau/Suffolk Counties

23.5.5 Late blight, Phytophthora infestans

Time for concern: Throughout the growing season and in storage

Key characteristics: The spores are commonly carried by wind, rain, and equipment. Lesions on leaves and stems become visible as small flecks within three to five days after infection. The infected tissue is initially water-soaked but becomes brown or black in a few days. Lesions are often surrounded by a halo of light green tissue. Under high humidity, sporulation is visible as a delicate, white mold surrounding the lesion. See References 1, 3, and 5.

*Management Option*		*Recommendation*
Scouting/thresholds		Watch fields for the development of late blight. Start applications of fungicides when plants are six to eight inches high. Continue applications throughout the season and until vines are no longer green. Use disease severity values to monitor disease favorable conditions throughout the growing season via the late blight network email group. Contact a local Extension office or IPM Specialist for information about access. See Reference 6.
Note(s)		Late blight fungus has developed a resistance to metalaxyl (mefenoxam).
Resistant varieties		Potato varieties differ slightly in their susceptibility, but commercial varieties do not have useful levels of resistance. The most susceptible varieties are: FL-1533, Monona, Atlantic, Superior, Norchip, and Shepody.
Site selection		Avoid fields that cannot be effectively sprayed.
Hilling		Proper hilling practices reduce the exposure of tubers to spores.
Vine-killing		Proper vine-killing practices reduce the exposure of tubers to spores.
Seed selection/treatment		Plant disease-free seed.
Postharvest		Monitor storage potatoes for infection.
Sanitation		Eliminate cull piles before plants emerge in the spring.
Crop rotation

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