July 10, 2000 Volume 9 No. 17 Update on Pest Management and Crop Development
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HUDSON VALLEY INSECTS OF NOTE |
(Dick Straub rws9@cornell.edu & Peter Jentsch pjj5@cornell.edu, Entomology, Geneva)
European red mite (ERM) are relatively scarce this season in most Hudson Valley orchards. As usual however, two-spotted spider mite (TSM) are very active and bronzing leaves. It is apparent that some miticides having good efficacy against ERM are not necessarily effective against TSM. The question of how to rescue blocks from TSM was answered last season by data from two trials at the Hudson Valley Lab. Under high TSM infestations (13 - 18 motiles/leaf, 3 AUG), we evaluated single sprays of most current miticides. AgriMek + oil (5 oz/100) produced 88.4% reduction of motiles - this material however, would be ill used as a rescue treatment, for a number of reasons. We were encouraged to find that Vendex 50W (8 oz/100) was highly effective, providing 98% reduction of motiles at 21 days postapplication. (We unfortunately did not include Kelthane in either trial - we are looking at it this season). Less encouraging results against TSM were provided by Pyramite (39% reduction) and Carzol (no effect). Vydate (16 oz/100) provided surprising efficacy (83% reduction), information that should help in those orchard situations requiring treatment for 2nd generation leafminer.
A remarkable note of this season is the dramatic increase in leafhopper populations. Rose leafhopper, which has been somewhere on vacation the last couple of seasons, has returned as a pest. The bigger story however, is potato leafhopper (PLH). We noted the first adult somewhat earlier than usual (5 JUN), and they have since built to unusually high numbers. Such populations of PLH present an array of control options and decisions.
Non bearing trees - Because rapid shoot extension is critical, leafhoppers, and PLH in particular, should be controlled. This is not always easy to accomplish, given that PLH are terminal feeders and elongating shoots rapidly produce new leaves that are not protected by previous insecticide sprays. Even quasi-systemic materials such as Provado do not provide residual protection. Control therefore, requires frequent applications to protect new foliage. If frequent applications (10-14 day schedule) are elected, it makes good economic sense to choose from any of the recommended contact insecticides for this purpose. Data from a recent trial however, suggests that Provado at the reduced rate of 0.5 oz/100 reduces hopper populations and protects new foliage reasonably well when applied on a 14 day schedule. Given that the recommended rate for leafhoppers is 1-2 oz/100, the reduced rate renders Provado more economically attractive.
Bearing trees - In our opinion PLH damage, although it may look bad, does not seriously affect either tree-growth or fruit-growth parameters. Shoot extension is not so important in bearing trees, and in fact, reduction of elongation or vigor may be desirable. A caveat to this philosophy however, is the potential role of PLH as vectors of fire blight. Because this disease has been prevalent this season, highly susceptible cultivars such as ‘Gala’ and’Ginger Gold’ etc., should be protected as much as possible from PLH feeding. This may be accomplished by frequent sprays as described above.
INSECTS WITH ISSUES |
(Art Agnello ama4@nysaes.cornell.edu, Entomology, Geneva)
There are many insects present in apple orchards that provide a benefit to growers by feeding on pest species. It is important that growers be able to recognize these natural enemies, so that they are not mistaken for pests. The best way to conserve beneficial insects is to spray only when necessary, and to use materials that are less toxic to them (see Tables 5 & 12, pp. 34 and 42 of the Recommends). This brief review, taken from IPM Tree-Fruit Fact Sheet No. 18 , covers the major beneficial insects that are likely to be seen in N.Y. orchards, concentrating on the most commonly seen life stages. Factsheet No. 23, "Predatory Mites" , reviews mites that are important predators of leaf-feeding mites.
This fly (Family Cecidomyiidae) is an aphid predator, and overwinters as a larva or pupa in a cocoon. Adults emerge from this cocoon, mate, and females lay eggs among aphid colonies. The adults are delicate, resembling mosquitoes, and are not likely to be seen. The eggs are very small (about 0.3 mm or 1/85 in. long) and orange. They hatch into small, brightly colored, orange larvae that can be found eating aphids on the leaf surface. These predacious larvae are present from mid-June throughout the summer. There are 3—6 generations per year. In addition to aphids, they also feed on soft-bodied scales and mealybugs.
The Family Syrphidae contains the "hover flies", so named because of the adults' flying behavior. They are brightly colored with yellow and black stripes, resembling bees. Syrphids overwinter as pupae in the soil. In the spring, the adults emerge, mate, and lay single, long whitish eggs on foliage or bark, from early spring through mid-summer, usually among aphid colonies. One female lays several eggs. After hatching, the larvae feed on aphids by piercing their bodies and sucking the fluids, leaving shriveled, blackened aphid cadavers. These predacious larvae are shaped cylindrically and taper toward the head. There are 5—7 generations per year. Syrphid larvae feed on aphids, and may also feed on scales and caterpillars.
• Stethorus punctum - This ladybird beetle is an important predator of European red mite in parts of the northeast, particularly in Pennsylvania, and has been observed intermittently in the Hudson Valley of N.Y., and occasionally in western N.Y. Stethorus overwinters as an adult in the "litter" and ground cover under trees, or in nearby protected places. The adults are rounded, oval, uniformly shiny black, and are about 1.3—1.5 mm (1/16 in.) long. Eggs are laid mostly on the undersides of the leaves, near the primary veins, at a density of 1—10 per leaf. They are small and pale white, and about 0.3—0.4 mm (1/85 in.) long. Eggs turn black just prior to hatching. The larva is gray to blackish with numerous hairs, but becomes reddish as it matures, starting on the edges and completing the change just prior to pupation. There are 3 generations per year in south-central Pennsylvania, with peak periods of larval activity in mid-May, mid-June and mid-August. The pupa is uniformly black, small and flattened, and is attached to the leaf.
• Other Ladybird Beetles - Ladybird beetles are very efficient predators of aphids, scales and mites. Adults are generally hemisphere-shaped, and brightly colored or black, ranging in size from 0.8 to over 8 mm (0.03—0.3 in.). They overwinter in sheltered places and become active in the spring. Eggs are laid on the undersides of leaves, usually near aphid colonies, and are typically yellow, spindle-shaped, and stand on end. Females may lay hundreds of eggs. The larvae have well-developed legs and resemble miniature alligators, and are brightly colored, usually black with yellow. The pupal case can often be seen attached to a leaf or branch. There are usually 1—2 generations per year. One notable species that is evident now is Coccinella septempunctata, the sevenspotted lady beetle, often referred to as C-7. This insect, which is large and reddish-orange with seven distinct black spots, was intentionally released into N.Y. state beginning in 1977, and has become established as an efficient predator in most parts of the state.
Adult lacewings are green or brown insects with net-like, delicate wings, long antennae, and prominent eyes. The larvae are narrowly oval with two sickle-shaped mouthparts, which are used to pierce the prey and extract fluids. Often the larvae are covered with "trash", which is actually the bodies of their prey and other debris. Lacewings overwinter as larvae in cocoons, inside bark cracks or in leaves on the ground. In the spring, adults become active and lay eggs on the trunks and branches. These whitish eggs are laid singly and can be seen connected to the leaf by a long, threadlike "stem". Lacewings feed on aphids, leafhoppers, scales, mites, and eggs of Lepidoptera (butterflies and moths).
There are many species of "true bugs" (Order Hemiptera) such as tarnished plant bug, that feed on plants, but a number of them are also predators of pest species. The ones most likely to be seen are "assassin bugs" or reduviids (Family Reduviidae), and "damsel bugs" or nabids (Family Nabidae). These types of predators typically have front legs that are efficient at grasping and holding their prey.
Parasitoids are insects that feed on or in the tissue of other insects, consuming all or most of their host and eventually killing it. They are typically small wasps (Order Hymenoptera), or flies (Order Diptera). Although the adult flies or wasps may be seen occasionally in an orchard, it is much more common to observe the eggs, larvae, or pupae in or on the parasitized pest insect. Eggs may be laid directly on a host such as the obliquebanded leafroller, or near the host, such as in the mine of a spotted tentiform leafminer. After the parasitoid consumes the pest, it is not unusual to find the parasitized larvae or eggs of a moth host, or aphids that have been parastized ("mummies"). Exit holes can be seen where the parasitoid adult has emerged from the aphid mummy.
There is a diversity of other beneficial species to be found in apple orchards, most of which are rarely seen, but whose feeding habits make them valuable additions to any crop system. The use of more selective pesticides helps to maintain their numbers and contributes to the level of natural control attainable in commercial fruit plantings. Among these beneficials are:
• Spiders (Order Araneae): All spiders are predaceous and feed mainly on insects. The prey is usually killed by the poison injected into it by the spider's bite. Different spiders capture their prey in different ways; wolf spiders and jumping spiders forage for and pounce on their prey, the crab spiders lie in wait for their prey on flowers, and the majority of spiders capture their prey in nets or webs.
• Ants (Family Formicidae): The feeding habits of ants are rather varied. Some are carnivorous, feeding on other animals or insects (living or dead), some feed on plants, some on fungi, and many feed on sap, nectar, honeydew, and similar substances. Recent research done in Washington has shown certain species (Formica spp.) of ants to be effective predators of pear psylla.
• Earwigs (Family Forficulidae): Although these insects may sometimes attack fruit and vegetable crops, those found in apple orchards are probably more likely to be scavengers that feed on a variety of small insects.
end of this issue
