Vegetable Insect Note 1
The pickleworm is the most destructive insect pest of cucumbers, summer squash and cantaloupes in North Carolina. For many years, it was unprofitable to grow cucumbers in mid or late season because of this pest. Technology exists that clearly demonstrates that a fall crop of cucumbers can be grown profitably. It is essential, however, to carry out an intensive monitoring program and a rigid treatment program using the proper insecticides, obtaining good coverage and following a 5 to 7 day schedule.
Although cucumbers are severly damaged some years, squash appears to be the preferred and favorite host. Squash flowers, furit and small plants become heavily infested while adjacent cucumber flowers and fruit may remain clean. Thus, squash has been used as a trap crop to attract moths as a detection tool as well as to saturate with insecticide. We are presently developing a sex pheromone monitoring system that will use a septa, the Harstack wirescreen trap and a forecasting network.
Low temperatures during winter kill these insects in N.C. The pest is re-established each year when moths fly back from south Florida. For this reason, the insect is seldom a pest until early July. Crops grown during the late summer and fall must be treated in 9 out of 10 years with insecticides to obtain marketable fruit. The effectiveness of insecticide control is enhanced by insect resistance in some varieties.
The most important economic damage caused by the pickleworm is to the fruit.
Young pickleworms usually feed for a time among small leaves at the growing tips of
vines or within blossoms. A favorite place is the large staminate flowers of
squash where larvae hide under the ring of stamens at the base of flowers. When
about half grown, pickleworms normally bore into the sides of fruits or stems and
continue to feed there, causing internal damage and producing soft excrement. Both
young and old fruits are attacked, but they prefer young fruits before the rind has
hardened. After the rind has been punctured the fruit soon becomes "sour".
As the infestation increases, young fruits and flowers are damaged. The growing vines sometimes become riddled and cease to grow.
The adult is an active night-flying moth that is seldom observed. Moths reared in cages spend most of their time during the day resting on the walls of the cages
with their hind wings partly exposed and the tips of the front wings touching the
walls. The tip of the abdomen bears a tuft of long hairlike scales. It is held
aloft and waved slowly in a circular movement. This gives the impression that it
is the creature's head bearing a shaggy mane.
Moths have a wingspread of about one inch. Both pairs of wings are margined with a 1/3 inch wide yellowish-brown band. The body is the same color with a purplish sheen. There is a transparent yellowish-white spot near the middle of each front wing and on the basal one-third of each hind wing.
Eggs are deposited singly or in small clusters on hariy spots on the plant such as blossoms and young leaves at the growing tips of vines. Eggs are hard to locate since they are thin walled and have no definite shape. At first they are white, but later they turn a dull yellow and look like pieces of beeswax.
After it hatches from the egg, the
larva is 1/16 inch long and the head
is wider than its body. It is almost colorless except for slightly darker jaws and
a black spot on each side of the head. Every segment has very
small dark tubercles, each containing
a long bristle. The larva grows rapidly and casts its skin 5 times during its
development.
In the third instar or developmental period, the larva reaches a length of about
1/4 inch and the tubercles are larger and darker so the characteristic spotted
pattern can be seen by the naked eye. In the fourth instar, the larva attains a
length of about half an inch, and the spots are almost black. When the fourth
instar skin is cast, a decided change takes place. The spots are lost, and the
fifth instar is at first plain white but soon turns pale green or pink. It retains
this color until it leaves the fruit and spins a cocoon in a fold of wilted leaf or
among dead leaves or trash on the ground.
The pupa is white at first but soon turns a reddish-brown. It develops in a cocoon consisting of a thin layer of silk attached to the leaf.
The total period between egg hatching and adult emergence was 17 days in tests conducted in Raleigh. Therefore, the period from egg deposition to adult emergence would average about 20 days under ideal conditions. In the fall, however, the life cycle is prolonged, the pupal stage alone taking more than 20 days.
These insects overwinter in semi-tropical areas such as southern Florida. Therefore, infestations depend upon flights of moths from the South. The first pickleworms of the summer usually appear any time from mid-June to mid-August (usually early July in most years). By August the number is increased and they continue to increase until low temperatures kill plants, insects, or both. There are two full generations of pickleworms, with a partial third, if food is available and there is no early frost. Of interest also is that survival of all stages of the pickleworm declines at temperatures above 85 degrees F.
In North Carolina, experiments in the field have shown very distinct differences in the susceptibility or resistance of squash varieties to pickleworms. The more resistant varieties are Butternut 23, Summer Crookneck, Early Prolific Straightneck, and Early Yellow Summer Crookneck. The more susceptible varieties are Cozini, Black Zucchini Caserta, Zucchini, Shrot Cofozella and Benning Green Tint Scallop. Many other varieties tested fall between these groups.
Tests with insecticides show much better control of pickleworms on resistant varieties than on susceptible varieties.
Cucumbers, cantaloupes and watermelons are less frequently and less destructively attacked than squash. When pickleworms are present, insecticide applications should be made.
A few plants of a susceptible squash variety are helpful in detecting the first
appearance of pickleworms, as evidenced by the insect's presence on flowers. A
regional and state pickleworm surveillance program using squash as a trap crop or
a sex pheromone trap throughout the Southeast is in various stages of development.
Insecticide applications should begin immediately when pickleworms or their damage appears. Make applications at weekly intervals after picking fruit but never just before. More frequent applications may be needed if populations and temperatures are high. Apply in early evening to minimize bee kills.
Application equipment that will ensure good spray coverage (hollow cone nozzle with drops and 200+ psi pressure) to developing fruit will give excellent control. Air blast sprayers also may be used.
For commercial plantings, consult the North Carolina Agricultural Chemicals Manual for the most recent recommendations. Commercial growers should always check with their buyers and processors before using any pesticide. Also, some pesticides may induce leafminers, spider mites or cabbage looper infestations. Do not exceed 3 applications of endosulfan per year.
In home gardens use the insecticides listed in the table below. Do not exceed 3 applications of endosulfan per year. Treat every 5 to 7 days from the time first injury is noted until the infestation is under control. A rigid treatment program is absolutely essential for late-season cucumbers, squash, melons and pumpkin.
| Insecticide and Formulation | Amount of Formulation per Gallon of Spray | Days to Harvest |
|---|---|---|
| carbaryl (Sevin) | ||
| 50 WP | 2 tblsp. | 0 |
| 80 WP | 1-1/4 tblsp. | 0 |
| 4 XLR | 2 tsp. | 0 |
| 5 D | -* | 0 |
| endosulfan (Thiodan, Phaser) | ||
| 50 WP | 2 tblsp. | 2 |
Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.
For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.
Published by North Carolina Cooperative Extension Service
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Web page last updated by M.J. Munster on 23 May 1996