Insect Control Strategies for Vine Crops
Insects attack vine crops from the time of seeding until harvest. They can reduce the stand, defoliate the leaves, feed on roots or flowers, transmit both bacterial and viral diseases, and create wounds that may help fungal pathogens enter the plant. There are 7 major insect pests to consider: seedcorn maggot, cucumber beetles, squash vine borer, green peach aphids, melon aphids, mites, and whiteflies. Growers need to protect the crop against insect damage while concurrently ensure pollination by bees.
SEED CORN MAGGOTS
Seed corn maggots have been an increasing pest in recent years. The amount of injury that these maggots inflict is related to root growth and soil temperature. When the soil is cool, feeding injury is more severe. When the soil is warm, root growth outpaces maggot feeding. Do not plant vine crops in cool soils. The adult flies are attracted to organic matter, so manure applications or plowing up cover crops should be done early - at least 1 month before planting. Completely covering transplant root balls may help. Adding a seed treatment in the hopper box is a good practice for direct-seeded crops. Banded soil-incorporated applications may be needed.
THE STRIPED CUCUMBER BEETLE
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 the drip irrigation reduced larval populations by about 50%. Black plastic mulch alone reduces the survival 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 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 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 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 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.
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.
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