Commercial Production of Pickling &
Slicing Cucumbers in North Carolina

Pest Management

Integrated pest management (IPM) is an approach designed to keep pest populations below economically damaging levels by using selected control tactics, including certain cultural practices, plant resistance, and chemical and biological control. With many pests, especially diseases and weeds, growers must use preventive control strategies to eliminate the potential for infection before the crop is established. In contrast, most insect pests can be controlled after a field is infested, and scouting fields for the presence of economically damaging insect populations is a good way to eliminate unnecessary pesticide applications. For most pests, a combination of one or more strategies is often required for successful control, and the crop must be closely monitored to determine the need and timing of various control practices.

Some logical steps to follow in an IPM program are identifying insects, diseases, and weeds; keeping records of pest problems, field locations, pesticides used, weather conditions, etc.; scouting and monitoring for pests to determine pest and action levels; proper selection, handling and disposal of pesticides; safe and effective application of pesticides; and an integration of any and all control tactics and strategies.

Some essential strategies for integrated pest management follow:

• Keep records
• Select adapted cultivars with disease resistance and insect tolerance
• Practice a 24-month, non-cucurbit crop rotation
• Select fertile, well-drained fields
• Sample fields annually for pH, nutrients, nematodes, soil insects, and weeds
• Use certified seed treated with fungicides and insecticides
• Seed ¹/₂ to ³/₄ inch deep on raised beds after soils warm to 60°F to "outgrow" pests
• Place bee colonies in fields after blooms are present
• Apply a general purpose fungicide shortly after emergence and include an insecticide as needed
• Diagnose all leaf spots and plant abnormalities promptly
• Use a high-pressure (200+ psi) sprayer
• Irrigate fields to ensure 1 inch of water each week
• Monitor migration of pickleworms with sex-pheromone trap and spray as needed
• Reapply nitrogen and potassium after leaching rain
• Harvest cucumbers three times a week
• Avoid injuries during harvesting and handling
• Use chlorine in all dump, wash, and handling water

Specific and more detailed information on insects, diseases, and weeds is readily available through local county Cooperative Extension centers. County agents and Extension specialists offer assistance with identification, farm tests, publications, control recommendations, and related advisory services.

Because pesticide regulations change rapidly, few materials and no application rates have been included in this publication. Ask county Extension staff for any additional information you need on cucumber pesticides or consult the North Carolina Agricultural Chemicals Manual for current materials and recommended rates. In all cases, follow directions on the pesticide label and use pesticides safely.

Weed Management

The major weeds associated with North Carolina cucumbers are common lambsquarters (Chenopodium album), annual and perennial grasses (Poaceae), pigweeds (Amaranthus species), common ragweed (Ambrosia artemisiifolia), common cocklebur (Xanthium strumarium), and annual morningglory (Ipomoea species) (Toth et al. 1994). Weeds are usually more prevalent in the spring cucumber crop than in the summer cucumber crop.

Weeds reduce cucumber yield and quality, and are hosts for insects (e.g., cucumber beetle), and animals (e.g., box turtles, mice, etc.). Stress caused by weed competition can also make cucumbers more susceptible to disease. Cucumbers must be maintained nearly (99-100%) weed free to prevent yield and quality reductions. For example, if 95% of the weeds in a field are controlled and 5% of the weeds are not, then up to a 50% yield or quality reduction may occur. Cucumbers are most vulnerable to yield loss to weeds between 14 and 32 days after emergence (Friesen 1978). Thus, cucumbers must be near weed free between 14 and 32 days after emergence to prevent reductions in yield or quality.

A specific weed management program must be developed for controlling weeds specific to each field. Successful weed management programs should include a well-planned and implemented strategy of cultural (e.g., cover crops, cultivars, plastic mulch), mechanical (e.g., two to three cultivations, one to two hand weedings) and chemical (e.g., preplant, preplant incorporated, preemergence, and/or postemergence herbicides) methods. Species identification, density, and control strategy must be known (Tables 12 and 13). Growers should record the weed species in each field and use these records to detect any weaknesses in the weed management program used from year to year. Once weaknesses or weed escapes are detected, then adjustments must be made in the weed management program to achieve control of these weeds.

Table 12. Weed Species, Density, and Control Strategies

	Severity of Infestation (Number of plants/100 square feet) b,c
	Scouting Time a	Light		Moderate		Heavy
		No.	Strategy	No.	Strategy	No.	Strategy
Annual Grasses
Crabgrass	Su, F	1-5	B	5-15	B	15	B
Goosegrass	Su, F	1-5	B	5-15	B	15	B
Barnyardgrass	Su, F	1-5	B	5-15	B	15	B
Fall panicum	Su, F	1-2	B	2-10	B	10	B
Johnsongrass (seedling)	Su, F	1-2	B	2-4	B	4	B
Crowfootgrass	Su, F	1-5	B,C	5-15	B,C	15	B,C
Broadleaf signalgrass	Su, F	1-5	B,C	5-15	B,C	15	B,C
Foxtails	Su, F	1-2	B	2-10	B	10	B
Annual Broadleaves
Common lambsquarters	S, Su	1-2	B	2-4	B	4	B
Carpetweed	S, Su	2-5	B	5-15	B	15	B
Common purslane	S, Su	2-5	B	5-15	B	15	B
Redroot pigweed	S, Su	1-2	B	2-4	B,C	4	B,C
Common ragweed	S, Su	2-4	B	4-8	B,C	8	B,C
Common cocklebur	S, Su	1-2	C	2-4	C,D	4	C,D
Prickly sida	S, Su	1-5	D	5-15	A	15	A
Morningglories	S, Su	2-4	D	4-8	A	8	A
Sicklepod	S, Su	1-2	D	2-4	A	4	A
Perennials
Common bermudagrass	Su, F	1-2	B	2-4	B,C	4	B,C
Johnsongrass (rhizome)	Su, F	1-2	B	2-4	B,C	4	B,C
Nutsedges	Su, F	2-4	A	4-8	A	8	A

^a Scouting procedures should be conducted the year or season before planting cucumbers. S = Spring; Su = Summer; F = Fall.
^b Number of specified weed plants in a 100-square-foot (10-by-10-foot) block.
^c Weed control strategies for
A = Avoid planting cucumbers if possible if land is fallow and weeds are perennials. Use glyphosate (Roundup) site preparation techniques or other effective herbicides the previous year if applicable.
B = Available herbicide programs plus cultivation will control this weed during the growing season. If infestation is light, cultivation alone may suffice. No action necessary in previous season.
C = Destroy before seeds mature by disking, mowing, hand pulling, and herbicide use. This will eliminate seed from current weed crop, but a reservoir of weed seed for this particular weed probably exists in the soil.
D = Same as C except none of the registered herbicides provide adequate control of this weed. If cucumbers are to be grown in this area, provisions for frequent cultivation, supplemented by hand hoeing, need to be made.

Table 13. Relative Susceptibility of Weeds to Suggested Registered Herbicides

	Herbicide and Time of Application  a
	Glyphosate	Paraquat	Prefar	Prefar + Alanap	Curbit	Alanap	Curbit + Alanap	Poast +Crop Oil
Species	PREPLANT	PREPLANT	PPI	PPI	PRE	PRE	PRE	POST
Weed
Annual Grasses
Crabgrass	E	E	E	E	E	G	E	E
Goosegrass	E	E	G	E	E	G	E	E
Barnyardgrass	E	E	E	E	E	G	E	E
Foxtails	E	E	E	E	E	G	E	E
Fall panicum	E	E	E	G	E	F	E	E
Broadleaf signalgrass	E	E	G	F-G	E	F	E	E
Crowfootgrass	E	E	G	F-G	E	F	E	E
Johnsongrass (seedling)	E	E	G	E	E	G	E	E
Annual Broadleaves
Common lambsquarters	E	E	E	E	E	E	E	N
Carpetweed	E	E	P	E	E	E	E	N
Common purslane	E	E	G	E	E	E	E	N
Redroot pigweed	E	E	G	G	E	G	E	N
Common ragweed	E	E	P	G	P	G	G	N
Common cocklebur	E	G	P	G	P	G	G	N
Prickly sida	E	G	P	P	P	P	P	N
Sicklepod	E	G	P	P	P	P	P	N
Morningglories	F-G	G	P	P	P	P	P	N
Perennials
Common bermudagrass	E	P	P	P	P	P	P	E
Johnsongrass (rhizome)	E	P	P	P	P	P	P	E
Nutsedges	G	P	P	P	P	P	P

Notes: E = 90% control or better. G = 76%-90% control. F = 50-75% control. P = 50% or less control. N = No control.

Relative ratings are based on the assumption that

• environmental (temperature, rainfall, etc.) and soil conditions are suitable for optimum herbicide activity.

• proper application techniques are used.

• proper rate adjustments are made for soil texture (depth, distribution, etc.).

• herbicides are used in accordance with labeled directions.

See current edition of North Carolina Agricultural Chemicals Manual for rates and recommendations.
^a PREPLANT = Paraquat should be applied before cucumber planting; with glyphosate allow at least 3 days between application and planting. Preplant herbicides are non-selective and kill emerged weeds.
PRE = preemergence (herbicide applied immediately after cucumber seeding). Preemergence herbicides prevent susceptible weeds from emerging.
PPI = preplant incorporated (herbicide applied and incorporated in soil before seeding cucumber). Preplant incorporated herbicides prevent susceptible weeds from emerging.
POST = postemergence (herbicide applied after weeds and cucumbers have emerged).

Insect Management

A number of insects can injure pickling and slicing cucumbers. Among these are aphids, flea beetles, seedcorn maggots, leafminers (Plate 9, Figure 11), spider mites (Plate 10, Figure 12), white flies, cabbage loopers, thrips (Plate 11, Figure 13), cucumber beetles (striped and spotted), squash bugs, squash vine borers, melonworms, and pickleworms. Beetles and pickleworms pose the most serious threats.

Correct identification and knowledge of the insect's l ife cycle are essential for effective control. County plant clinics and the North Carolina State University Plant, Disease, and Insect Clinic can assist with identification. More detailed information on insect biology is in "Insect and Related Pests of Vegetables" (Sorensen and Baker 1994).

Two critical periods for insect activity are the prebloom stage for seedcorn maggots and cucumber beetles, and the flowering stage for pickleworms.

Fig. 11. Vegetable leafminer. From left to right; Adult, larva, and pupa.

Fig. 12. Two-spotted spider mite lifestages.

Fig. 13. Thrips adult.

Plate 9. Leafminer damage.

Plate 10. Spider mite damage. Note webbing and mites between leaf lobes.

Plate 11. Thrips injury.

Seedcorn maggot (Hylemya platura) is a primary cause of poor stands in cool, wet springs and especially on heavier soils with an abundance of nondecomposed plant trash. First evidence of this pest's presence will be wilted plants or malformed cotyledon leaves. Maggots can be found either inside the old seed or in young plants. They are legless, whitish insects about to inch long (Figure 14). The adult seedcorn maggot resembles the common housefly and can be found in a characteristic death position with its legs attached to objects such as limbs, posts, wire, or tall grass. Insecticide-treated seed, application of soil insecticide, or both can help control these pests. Proper planting depth at optimum soil temperatures promotes rapid germination, plant establishment, and growth, all of which overcome attack by seedcorn maggots.

Cucumber beetles, striped (Acalymma vittatum) (Plate 12) and spotted (Diabrotica unldecimpunctata howardi) (Plate 13), overwinter as adult beetles and are one of the first insects to attack young cucumber plants in the spring (Plate 14). In addition, this pest deposits eggs in the soil and around young plants in large numbers. The young larvae feed on plant roots and stems. These insects, known as rootworms, are common on field corn. Adults are known to be primary transmitters of bacterial wilt (Plate 15) and cucumber mosaic virus. Growers should check fields for adult beetles during the cotyledon stage to assess pest status and implement control strategies. Traps containing attractants and killing agents can be used to monitor beetles as well as to offer some control. Control most often requires the application of an insecticide. Rapid germination and plant establishment are significant factors in reducing the severity of beetle attack. The bacterium that causes bacterial wilt overwinters in the adult of this beetle.

Pickleworm (Diaphania nitidalis) is the most destructive insect pest of cucumbers in middle and late summer. Each year, migration of adult moths from areas south of North Carolina provides initial infestations. These populations become larger as the insects pass through their life cycle and go through four to five generations per season (Plate 16).

Pickleworms often pass unnoticed inside fruit, and may not be found until after the fruit is harvested or processed. Buyers and processors have zero tolerance for pickleworm.

Worm-like larvae first attack buds and tender terminals and later complete their growth in fruits or stems (Plate 17). Young larvae have many black spots scattered over their bodies. Full-grown larvae are green or coppery with brown heads. The adult pickleworm can be confused with melonworm (Plate 18). Melonworm adults have white hind wings while larvae have white body stripes and feed on the surface of the fruit (Plate 19).

The pickleworm can be controlled with timely and thorough applications of insecticides. Be careful that ends of rows and rows adjacent to woods or ditch banks are well covered with insecticides. In general, after July 15, growers should begin spraying just before any blooms open in a given field. When pickleworm sex-pheromone traps are employed, growers can begin and continue sprays as long as moths are collected (Figure 15). Growers can detect pickleworm early by close and periodic examination of young, tender vines. Squash is the preferred host of this insect, and a row of squash planted nearby and inspected regularly provides a good way to detect initial infestations of pickleworm. Apply insecticides at five-day intervals, always after picking. Check the insecticide label for rates and time limitations before harvest. Apply sufficient volume of water (30 to 100 gallons per acre) with high-pressure (200+ psi) and hollow-cone nozzles. This will ensure thorough coverage and provide continual protection to the developing plant. Apply insecticides in the evening (after 4 p.m.) for best results and minimal loss of pollinating insects.

With a sex-pheromone monitoring system for pickleworm moths in the final stages of development, a forecasting network throughout the southeast can be established. This network will monitor moth presence and absence and determine relative populations over time. This will eliminate unnecessary sprays and improve the time of essential sprays. This sex-pheromone trapping network should be available within the next several years and will be a welcome addition to cucumber integrated pest management.

Field selection. Select fields that are well drained, fertile, warm, and have good aeration. Avoid fields near other cucurbit crops (see Site Selection and Preparation section).

Sanitation. Avoid cultivating or harvesting while the cucumber plants are wet. Immediately after the last harvest, disk the field to promote rapid decay of the crop and destruction of disease-causing pathogens.

Soil treatment. Surveys have shown that most sandy soils in commercial cucumber production in eastern North Carolina should be treated with a nematicide. Growers should always follow chemical label directions. Soils can be sampled and assayed to determine the need to treat for nematodes. Sampling should be done in the fall of the preceding year for the spring crop, and in late spring for the upcoming fall crop. Time of sampling is critical to obtaining reliable results.

Seed selection. Always purchase seed from a reliable seed source. Insist that the seed be produced under disease-free conditions and treated with a protective fungicide and insecticide. Select cultivars that have as much disease resistance as possible, consistent with horticultural and market requirements (see Pickling Cultivars and Slicing Cultivars sections).

Specific Diseases and Their Control

Angular leaf spot is caused by the seed-borne bacterium Pseudomonas syringe pv. lachrymans which causes straw-colored spots with well-defined angular shapes on leaves (Plate 20). The organism occasionally attacks the fruits and may cause rotting. The disease is favored by cool, wet weather. There are resistant cultivars. Two pickling cultivars with resistance are Endeavor and Freemont, however these cultivars are shorter than most cultivars used by the processing industry. Sprays with a copper fungicide may be beneficial.

Anthracnose is caused by the fungus Colletotrichum obiculare that may be seedborne and may live for one or more years in the soil on crop debris. Leaf spots are light brown or salmon colored with irregular margins (Plate 21). The centers of the spots tend to drop out. Stems and fruits are also affected but this is rare in North Carolina. The disease is favored by warm, wet weather. Most cultivars recommended have some level of resistance (Tables 1 and 2). However, cultivar resistance is not always satisfactory under severe disease pressure. A two-year crop rotation with non-cucurbit crops is an essential practice and often must be supplemented with a regular spray program, especially for mid- and late-season crops.

Bacterial wilt is caused by the bacterium Erwinia tracheiphila that causes a progressive wilting of the plant and subsequent die-back of the vines (Plate 15). The disease is easily recognized in the field. Individual wilted plants occur randomly which reflects beetle transmission. Often, only a single vine or half a vine will wilt, indicating the point of infection by the beetle.

To confirm diagnosis, cut off a portion of the wilted runner near the first wilted leaf. Check for the presence of bacteria in the vascular system by cutting the stem piece in half. Realign the two cut surfaces, press together, and slowly separate to about 0.1 inch. The test is positive for bacterial wilt if thin slime strings are seen between the two cut surfaces (Plate 15). Normal sap (e.g., without bacteria in it) will not form a slime string. Try several samples on different plants. This disease is present throughout the state.

The bacterium overwinters in cucumber beetles and is spread by them. Most cultivars recommended do not have bacterial wilt resistance; some notable exceptions are Marketmore 80Bw (slicing type) and County Fair 87 (pickling type). Bacterial wilt can be prevented by controlling cucumber beetles with timely sprays of insecticides when beetles are present.

Cercospora leafspot and target spot. Cercospora leafspot is caused by the fungus Cercospora citrullina and causes pale spots on leaves surrounded by a dark ring and a chlorotic halo. A similar disease, target spot, is caused by the fungus Corynespora cassiicola. Target spot (Plate 22) produces a similar but more angular leaf spot. Both diseases are favored by wet and warm weather and are controlled by timely fungicide sprays.

Damping-off and seed rot can be caused by Pythium spp., Fusarium spp., Rhizoctonia solani, other fungi, and bacteria. Symptoms consist of poor emergence caused by seed decay in the ground and rot of the seedling at or near the soil surface. These result in spotty stands of plants. Most often damping-off and seed rot are problems during cool, rainy weather and are especially serious where water does not drain freely from a field and seed germination and seedling growth are delayed or inhibited. There are no resistant cultivars. Application of a soil fungicide or broad-spectrum soil fumigant before seeding may be helpful in problem fields.

Downy mildew is caused by an air-borne fungus Pseudoperonospora cubensis (Plate 23), the spores of which are blown northward each spring from overwintering areas in warmer climates. The fungus usually appears in mid-summer. Characteristic symptoms are yellow spots with a purplish, downy growth on the underside of leaves. The disease can be a problem during rainy periods after mid-season. Most commercial cultivars are highly resistant, which is especially useful in late summer and fall (Tables 1 and 2). Growers should follow a good fungicide spray program.

Fruit rots are caused by different soil-inhabiting fungi such as Pythium spp. (cottony leak) (Plate 24) and Rhizoctonia solani (belly rot) that affect fruit in the field and after harvest (Plates 25 and 26). Fruit rots are favored by wet weather. Harvested fruit should be cooled as soon as possible. There are some cultivars and breeding lines with moderate resistance to belly rot. Marketmore 76 (slicing type) is the most resistant (Uchneat and Wehner 1998). Fungicidal sprays may be helpful.

Gummy stem blight is caused by two related fungi (Didymella bryoniae and Phoma cucurbitacearum) that can be seed borne and overwinter on old plant material in the soil. Symptoms are large, dark brown spots that often appear on the leaf margin (Plate 27), and lesions on the stems. The disease is favored by wet weather and there are few cultivars with some resistance. The cultivar Slice (slicing type) is the most resistant to gummy stem blight.

Mosaics are caused by different viruses (cucumber mosaic [CMV], watermelon mosaic [WMV], papaya ringspot [PRSV-W], squash mosaic [SqMV], zucchini yellow mosaic [ZYMV]), and tobacco ringspot [TRSV] and tomato [TmRSV] ringspot) and usually are only minor problems in North Carolina. Symptoms vary considerably, but plants are usually stunted, their leaves and fruits mottled and distorted (Plate 28). Occasionally plants appear to outgrow symptoms. The viruses are usually spread by aphids. Most recommended cultivars are resistant to cucumber mosaic (Tables 1 and 2), while some slicer cucumber cultivars also have resistance to other viruses (Table 2). In western North Carolina, soils should be treated for nematodes to control TRSV and TmRSV. In all cases, growers should follow a good insect control program. Use of reflective plastic mulches and stylet oil sprays may reduce the incidence of aphid-borne viruses.

Powdery mildew is caused by the fungus Sphaerotheca fuliginea and occasionally by Erysiphe cichoracearum and is rarely a problem in North Carolina because most commercial cultivars are resistant. Powdery mildew can be recognized by a white, superficial, powdery growth that usually starts on the underside of older leaves (Plate 29). The disease can spread rapidly on all green plant surfaces except the fruit. Unlike many other diseases, powdery mildew may develop rapidly during dry weather. Management of the disease is based on growing resistant cultivars and spraying of a recommended fungicide if necessary.

Scab is caused by the fungus Cladosporium cucumerinum and produces dark gray, crater-like spots on fruits. On the leaves, spots are irregular with yellow margins and brown centers. The disease is favored by cool, moist weather and is a problem primarily in western North Carolina. Resistant cultivars are essential in that area. Most recommended cultivars have resistance (Tables 1 and 2). Management of the disease is based on a two-year crop rotation with non-cucurbit crops and a fungicide spraying program.

Root-knot is caused by soil-borne parasitic nematodes (Meloidogyne spp., especially M. incognita) which cause swellings or galls on the roots (Plates 30 and 31). The disease is more common and serious on sandy soils than on clay soils; crop injury is more serious during dry seasons than seasons with adequate rainfall. Root-knot is one of the most common and serious diseases of cucumbers in North Carolina (Main and Gurtz 1989), and all growers should practice control measures. Soils can be assayed for nematodes by the Nematode Advisory Section (there is a nominal fee per sample). Send samples to

Agronomic Division, Nematode
N.C. Department of Agriculture & Consumer Services
4300 Reedy Creek Road
Raleigh, NC 27607-6465

Private laboratories can also assay soils for nematodes.

Growers should treat soils with a nematicide, if recommended. Currently, there are no resistant commercial cultivars.

Sprayers

Adapted from Sumner and Sneed 1994.

Sprayers are used for applying insecticides, fungicides, herbicides, and foliar fertilizers. Boom sprayers, with the aid of drop nozzles, provide better coverage of the plant canopy than air-blast sprayers.

Most materials applied by a sprayer are in a mixture or suspension. Continuous agitation is needed when applying pesticides that settle out, even when moving from field to field or when stopping for a few minutes. Jet or mechanical agitators may produce that agitation.

Three factors to consider in selecting the proper pump for a sprayer are

1. Capacity — The pump should be of proper capacity or size to supply the boom output and to provide agitation (5 to 7 gallons per minute (gpm) per 100-gallon tank capacity).
2. Pressure — The pump must produce the desired operating pressure for the spraying job to be done. Pressures are indicated as pounds per square inch (psi). Piston or diaphragm pumps are recommended because they achieve high pressure.
3. Resistance to corrosion and wear — The pump must be able to withstand the chemical spray materials without excessive corrosion or wear. Use care in selecting a pump if wettable powders are to be used, as these materials will cause pump wear.

Nozzle tips are the most neglected and abused part of the sprayer. Because clogging can occur when spraying, nozzle tips and strainers should be cleaned and tested before each application. When applying chemicals, proper ground speed, operating pressure, and boom height should be maintained. This will ensure proper delivery of the recommended amount of pesticide to the plant canopy. Use a flat-fan nozzle to apply broadcast herbicides. When applying insecticides and fungicides, use solid or hollow-cone nozzles.

When applying insecticides and fungicides, completely cover both sides of all leaves with spray. Properly selected nozzles should be able to apply 25 to 125 gallons per acre when operating at a pressure of 60 to 200 or higher psi. Sprayers should be calibrated at 2 to 4 miles per hour. Calibration should be conducted every 8 to 10 hours of operation to ensure proper pesticide application. A good calibration procedure is given in the section entitled "Calibration of a Field Sprayer" in the North Carolina Agricultural Chemicals Manual, available through your county Extension Service center.