IPM in Cucumber

INTEGRATED PEST MANAGEMENT (IPM) is the blending of all effective, economical, and environmentally sound pest control methods into a single but flexible approach to managing pests. Those who practice IPM realize that it is neither possible nor economically feasible to eliminate all pests; instead pest populations should be managed below economically damaging levels. Users of the IPM approach recognize and understand the importance of the controls provided by nature. When human intervention is necessary, the least invasive practices, such as plant resistance, biological control, and cultural control, should be used because these are the practices that fit best into sustainable agriculture. Highly disruptive or environmentally damaging practices should be used only as a last resort. Chemical pesticides should be used only when necessary, based upon frequent and routine monitoring of pest populations. Natural enemy populations should also be monitored so that their impact on pests can be determined. When pesticides are necessary, if possible, only those products should be used that are not detrimental to natural enemies. Integrated pest management is a dynamic and evolving practice. Specific management strategies will vary from crop to crop, location to location, and year to year, based upon changes in pest populations and their natural controls. As specific new approaches are developed, these too can be incorporated into the program as appropriate. Modern pest managers will be most effective if they are knowledgeable about their pests, beneficials, and all of the control options available. Weeds Herbicides registered for use on cucumbers do not provide total, season long control. Successful weed control requires integrating cultural and chemical methods. Preplanting control of perennial weeds is essential. Cucumbers should be planted to land where the annual weed seed population has been reduced by cultural procedures such as crop rotation, summer fallowing or stale seedbed. Cultivation will be required to supplement chemical weed control. Many growers use plastic mulch in the production of cucumbers. Opaque plastic can be used to control weeds in the row in main crop cucumbers. Contact your local agriculture office for information on controlling weeds growing between the rows of plastic mulch. Care must be taken to avoid fields where residual herbicides from previous years persist in the soil as crop injury may occur. Diseases Damping off (fungi) Characteristics: (Fusarium, Rhizoctonia, Pythium, Phytophthora sp.) Occurs in areas with poor drainage or areas with a previous history of the disease. Damping-off is often associated with high humidity and high temperature. The temperature range in which these fungi can live is quite broad, from about 12 to 35oC with an optimum (the temperature at which damping-off develops fastest) of 32oC. That is why you can find damping-off disease both in highlands with a temperate climate and in (sub) tropical lowlands. Control: Sow seeds treated with a fungicide. For greenhouse grown plants, sterilize soil (or use an artificial mix) and disinfect work areas, benches, flats, etc. Drench seedlings with an appropriate fungicide. Leaf Spots - Alternaria (fungus), angular (bacterium) Characteristics: Alternaria causes small circular spots which enlarge up to 2 cm in diameter with dark concentric rings within the spots. Spots coalesce to affect large areas of the leaf. Angular leaf spot causes small angular spots that are irregular in shape and size. May attack fruit causing water soaked spots. Fruit rot follows. Both organisms overwinter on the seed or in plant residue in the soil. Control: Follow a 1 to 2 year rotation. Apply a fungicide at first sign of disease and at 7 to 10 day intervals. Use an alternating schedule with an organic fungicide for Alternaria and fixed copper for angular leaf spot. Powdery Mildew (fungus) Characteristics: Appears as a white powdery growth on leaves which may cause leaves to wither and die. It tends to be a problem in some varieties more than others. It is favored by high temperatures. Control: Resistant cultivars are available. For susceptible cultivars apply an appropriate fungicide at the first sign of the disease and at 7 to 10 day intervals. Downy Mildew(Pseudoperonospora cubensis) Symptoms of downy mildew are first evident as small, slightly chlorotic to bright yellow areas on the upper leaf surface. The color is less vivid on the corresponding lower leaf surface. Lesions appear first on the older crown leaves and appear progressively on the younger, more distal leaves as these leaves expand. As the lesions expand, they may remain chlorotic or yellow or become necrotic and brown. Lesion margins are irregular on most cucurbits, but on cucumber they are angular and bound by leaf veins. Cucumber Scab (fungus) Characteristics: A fungal disease which overwinters in seed and in crop residue. Infected fruit will have dry, sunken corky areas up to 1 cm in diameter. Scab areas on leaves will cause misshaped leaves. The disease is brought on by moist, humid conditions and cool night temperatures. Control: Use resistant cultivars. No cultivar is completely immune so follow a 2 year crop rotation. Effective fungicides are also available. Bacterial Wilt (Bacterium) Characteristics: (Erwinia tracheiphilia) The bacterial wilt organism apparently overwinters in cucumber beetles. Wilt appears on a low percentage of plants. Bacterial wilt is more severe with adequate to excessive levels of balanced nutrients than with deficient levels. It is promoted by low nitrogen and potassium levels in unbalanced nutrient situations. Control: Apply insecticides to control the cucumber beetles. Mosaic (virus) Characteristics: Several mosaic viruses may infect cucumber. Cucumber mosaic virus (CMV) is the most important. CMV infected plants are stunted, and new leaves are dwarfed, mottled and sometimes distorted. Fruit exhibits a yellowish-green mottle. The virus overwinters in perennial weeds such as milkweed, ground cherry, pokeweed, motherwort and chickweed. Aphids and sometimes cucumber beetles transmit the virus. Control: Grow resistant cultivars. Control aphids and cucumber beetles. Eliminate reservoir weed hosts within and surrounding cucumber fields. Insects Seedcorn Maggot Characteristics: Small yellowish-white maggots 6 mm long with a pointed head end. The adult is a small grayish-brown fly. Maggots feed on seed, causing seed to produce a poor plant, and will also feed on roots, causing poor plant growth. Seed corn maggots frequently attack deeply planted seeds. Control: Plant as shallow as needed in a well prepared seedbed. Early germination is necessary to get good plant stands and prevent injury. Later planted crops are not as susceptible to this pest. Good weather conditions are necessary to completely control the pest. Avoid planting susceptible crops in fields recently manured. Chemical seed treatment is essential. Cutworms Characteristics: Cutworms are dull colored, soft bodied caterpillars found at the base of plants, just under the soil level. They feed on seedlings, cutting them at soil level or just below. Control: See Atlantic Provinces "GUIDE TO PEST MANAGEMENT" for vegetable crops. Cucumber Beetle Characteristics: The striped cucumber beetle overwinters in the adult stage under leaves or dense grass, emerging in May or early June. The adult is 5 mm long. Its upper surface is about equally black and yellow, with the folded wing covers bearing three black stripes. Hot, humid weather favors the beetle feeding. Two weeks after emerging, the beetles mate and lay eggs. The orange-yellow eggs are laid in the soil at the base of host plants and hatch within 10 days. Upon hatching, the larvae burrow into the soil and start to feed on roots. Two weeks later, a new generation of beetles appear. In Canada, there is only a single generation per year. They are a carrier of bacterial wilt. Control: Apply insecticides when insects first appear and repeat as necessary. If not controlled this insect may cause a lot of damage. Two-Spotted Spider Mite Characteristics: An occasional pest but when it does occur, it can be serious. Leaves become speckled and then turn bronzed or brown. A fine webbing is produced on the underside of the leaves. The mites are microscopic in size. Usually this pest only becomes a problem under very hot dry weather conditions. Control: Apply appropriate miticide. Tarnished Plant Bug Characteristics: Small 6 mm long insect, mottled white and yellow with touch of black on wings. Nymph is very small, greenish-yellow and marked with black dots on the thorax and abdomen. They overwinter under bark or leaf-litter, emerging early in the spring and feeding on weeds and fruit buds. After mating, eggs are laid on stems and petioles. Nymphs (yellowish-green, 1 mm long) emerge after 10 days, undergoing two molts to become adults within 3 to 4 weeks. Adults and nymphs are equally damaging. Control: Apply insecticides when insects first appear and repeat as necessary. PESTS The striped cucumber beetle is our most serious insect pest. Overwintering adults invade in large numbers, transmit a bacteria that causes bacterial wilt, defoliate, lay eggs that result in larval feeding on roots, and go through 2 generations. Our ELISA data estimates that that about 5 to 10% of the overwintering adults carry the bacterial pathogen, and most of the transmission occurs from defecation into wounds. When we have looked for the bacteria inside the beetle, we find it associated with the hindgut. The carrying rate can go up to 70% in some cases. The amount of bacterial cells put into a plant determines how fast and severe the disease symptoms will be. Disease progress is made worse when beetles congregate on plants, because then more feces, and thus more bacterial cells, get moved into wounds. New methods of chemical control are on the horizon for cucumber beetles. Effective materials are listed in the Commercial Vegetable Production Guide. Biological and cultural controls also effect the striped cucumber beetle. A tachinid (fly) parasitoid of the adults occurs naturally in Pennsylvania, and was measured at fairly high levels in New York. Entomopathogenic nematodes can help as a biological control of the larvae feeding on the roots. One species ( Steinernema riobravis ) introduced through thedrip irrigation reduced larval populations by about 50%. Black plastic mulch alone reduces thesurvival rate of the larvae, perhaps by as much as 50%. Yellow mulch, however, attracts the adults. Row covers are effective against beetles, vine borers, and squash bugs, but they must be removed during flowering to allow for pollination. APHIDS Aphids are often controlled adequately by natural enemies until late in the season, unless you are in an area that has had problem with virus. If virus has not been a concern in your area, then it helps to limit insecticides to encourage natural enemies. You can find aphid mummies,lady bird beetles, and lacewing predators. However, if virus has been a problem, deterring aphids from moving into fields with reflective mulches, using resistant varieties when available and preventing movement of aphids from weeds or among different plantings becomes very important. Successive plantings make it harder to control virus transmission, as the vectors that build in one crop move onto the next. Also, both the green peach and the melon aphid have shown problems with insecticide resistance. Careful follow-up scouting after a spray is important, and be prepared to try other classes of insecticides. SQUASH VINE BORER Squash vine borer has one generation a year. Problems are typically more severe in squash, pumpkins and gourds than melons or cucumber. Scouts can look for the brightly colored moths flying during the day, frass at entry holes, or use pheromone to determine when they are flying. However, pheromone traps used in small planting may make problems worse by attracting moths that lay eggs singly among the fewer plants. Small plantings result in eggs being concentrated onto fewer vines. Timing insecticides to when the eggs are hatching and the larvae are very young is the key to control. SQUASH BUGS Squash bugs are more likely to be a problem in squash and pumpkins. Scouting is best directed at the coppery-brown eggs, and control directed against nymphs. Getting thorough coverage underneath leaves is essential. The insects are well protected under the large leaves of vine crops. Make sure you are not moving into canopy closure with a population of squash bugs. Scouting at early flowering helps. MITES Mites require large populations to cause serious damage, but their populations build up very quickly when temperatures are hot (>80F). Dry weather (<50% RH) also is correlated to mite build-up. They can complete development in only 5-7 days under these conditions, which is 2 to 3 times faster than many of our other vegetable pests. Often mites move in from nearby crops or weeds, and initial densities are high near field edges. WHITEFLIES Whiteflies are an occasional pest in Pennsylvania, but where they occur, they can also build up to very high densities. The species we have do not overwinter well in Pennsylvania, and typically move in from greenhouse material, or from other crops with whiteflies. POLLINATION Vine crops have 2 types of flowers: cucumbers, squash, pumpkin and watermelon have separate male and female flowers, while muskmelon have male and hermaphroditic (bisexual) flowers. While managing to stop pest damage, growers must also manage to support pollination by bees. The dense and sticky pollen needs to be transferred to the female flowers to ensure fruit that is well shaped, and to optimize yield. Fruit size and shape is related to the numbers of seeds produced, and each seed requires 1 or more pollen grains. Flowers are usually open and attractive to bees for only 1 day, and pollination must take place on the day that the flower is open. Ensuring the presence of 1 to 2 honeybee colonies per acre, and up to 3 hives per acre, has been the most reliable method of pollination in the mid-Atlantic. Colonies should be strong: at least 1,200 square inches of brood per colony and enough adults to care for them. Vine crops are not especially attractive to honeybees. Moving colonies into fields after blooming has started helps ensure that the bees work the vine crops. When bees are in the field, insecticides should only be applied near the evening, when the bees have returned to the colony. Notifying beekeepers and written contracts are good practices. Control Methods: • Use a portable vacuum to get the adults in the early evening. Put them right into a plastic bag, seal it and dispose of them. • Try placing cuttings of the tansy plant as a mulch in-between rows in the garden. • Spread any type of onion skins on the soil around the planted areas. • Consider building a bat habitat: Bats are predators of a wide range of pest insects, including cucumber beetles. • Make a trench 3" deep by 3" wide filling it with wood ashes. Moisten it so it won't blow away and don't let it get on the plants. Ashes can be toxic to plant foliage! • A deep mulch of straw helps by keeping the adults from walking plant to plant. Heavy mulching can deter cucumber beetles from laying eggs in the ground near plant stems and may hinder feeding by larvae migrating to fruits. This cultural control method, however, does not protect the leaves against attack from adult insects. Injury to fruit by tunneling of larvae is dependent on very moist soil as fruits ripen. Limiting irrigation at this time can minimize damage • Plant white varieties of radishes or rattail radishes with your cucumber plants to repel the beetles. Rattail radish roots are not edible but the seed pods are! • Mix a spray of 1 ounce wood ashes, 1 ounce hydrated lime and 1 gallon water. Spray upper and lower leaf surfaces. Hydrated lime is a powdered substance. Or use a spray of hot peppers, water and garlic. • Trellising plants can make leaves less accessible to insect larvae and may decrease egg-laying. Like mulching, trellising does not protect plants against attack by adult insects • Plant radish seeds right in the hills with the cucumber plants. • Floating row covers are an effective control method during the early season of plant growth. They prevent insect attack by forming a barrier between insects and plants. Row covers need to be removed during the late vegetative stage, at the onset of flowering, to allow for bee pollination. Once floating row covers are removed, other control measures such as treatments with botanical pesticides should be employed. • To fool cuke beetles: flatten a square of aluminum foil around the base of plants to bounce light on the undersides of leaves. This also helps the plants in giving them more light. • Plant any type of beans with cucumber. • Cultivate in the fall to expose the eggs. • If the infestation is beyond control use either of the botanical poisons: pyrethrum or rotenone. You want to hit the adults with these when you observe them feeding on pollen in flowers. • Sticky Traps: For the home gardener and small scale growers these can be an effective monitoring tool and a control! Cut some plywood board into rectangles 8 inches by 10 inches. Cardboard could also be used. Paint with yellow paint and coat with Tanglefoot or some other adhesive. Now what you want to do is to bait these traps specifically to trap cuke beetles. You can use pieces of cotton wicks stuck to the boards that have been soaked in a Eugenol based oil which is what attracts the female beetles. 2 types of oils that contain 60 to 90 percent eugenol are allspice oil and clove oil. Squash blossoms contain indole which are very attractive to the adults. If you can spare some you might mash them up and stick them to your trap. Stake your traps vertically at ground level or no more than 12 inches above. As the traps fill up you can scrape and recoat them until they become unusable. • Nematodes: Hexamermis spp. parasitizes the adults. Studies have indicated up to 90% of a population of cuke beetles being infected by the nematodes. Apply beneficial nematodes to kill the adults in mulch, seed furrows and around plant roots. • Neem Oil: Neem oil, which can act as an ovicide, can be used as a soil drench to treat eggs and larvae. It does seem to help with control of the adults as a repellant and antifeedant. Further tests must be done using Neem but it does look promising.