Scaffolds 01 index

(Dick Straub rws9@cornell.edu& Peter Jentsch pjj5@cornell.edu, Entomology, Highland)

All growers remember last year's severe infestations of potato leafhopper (PLH). Damage by this migratory pest is usually worse when it shows up early -- they arrived early again this season. PLH can cause significant damage to newly planted trees that are not yet established. In general, though, we feel that PLH infestations are not harmful to established bearing trees. When PLH, white apple leafhopper (WALH), rose leafhopper (RLH) and aphids are present, however, control measures are often warranted. That scenario is now, or will soon be present in most Hudson Valley orchards.

Newly hatched White appple leafhopper nymph

Knowing from earlier lab studies that Provado is very effective against leafhoppers, we performed field trials last season to evaluate reduced rates of this insecticide against all three species of leafhoppers. This research was prompted because PLH are terminal feeders (on new growth only) and constant reinfestation of new foliage is the norm; therefore, when trees are vigorous, untreated foliage is often available within hours after application of an insecticide. This obviously computes into wasted dollars. The same rationale can be applied to aphids, which are also terminal feeders.

We applied Provado in combinations at a full rate (2 oz/100 gal) and a quarter rate (0.5 oz/100 gal), at varying intervals (3rd-5th cover). We monitored nymphs of PLH/WALH/RLH and leaf damage by PLH.

Performance of Reduced Rates of Provado, HVL - 2000

*3rd Cover - 6/13; 4th Cover - 6/23; 5th Cover - 7/4

Because of Provado's translaminar activity, all rates and schedules produced excellent control of WALH/RLH nymphs (however, reduced rates will not control leafminer). Against PLH nymphs, the number of applications was shown to be more important than rate; i.e., better protection of new foliage. Considering the percentage of leaves with PLH damage, the number of applications again appeared to be more important than application rate.

PLH FOLIAR DAMAGE

Although data on aphids were not taken, we know that Provado is an excellent aphicide, and the same principle would hold as for PLH -- maintaining coverage of new growth is more important than rate. Moreover, reduced rates are likely to increase the survival of cecidomyiid and syrphid predators that are common and effective biological control agents.

In the table above, we estimated the relative costs per acre that would be attributed to each schedule. Reduced rates of Provado will provide comparable control of the foliar-feeding pests described, and could result in a significantly lower spray bill. Note: NYS-DEC recently revised its interpretation of a FIFRA 'Section 2(ee)' recommendation, so that now a pesticide may be used for agricultural purposes in a dosage, concentration or frequency less than that specified on the labeling without having a Section 2(ee) issued for that use.

(Art Agnello ama4@nysaes.cornell.edu & Harvey Reissig whr1@nysaes.cornell.edu, Entomology, Geneva)

Green Aphids: Apple aphid, Aphis pomi De Geer, Spirea aphid, Aphis spiraecola Patch

Although small numbers of these aphids may be present on trees early in the season, populations generally start to increase in mid- to late June. This trend has been evident once again this year, as the plentiful rains and recurring heat have resulted in a profusion of succulent terminal growth much favored by these insects. Large numbers of both species may build up on growing terminals on apple trees during summer. Both species are apparently common during the summer in most N.Y. orchards, although no extensive surveys have been done to compare their relative abundance in different production areas throughout the season.

Nymphs and adults of both species suck sap from growing terminals and water sprouts. High populations cause leaves to curl and may stunt shoot growth on young trees. Aphids excrete large amounts of honeydew, which collects on fruit and foliage. Sooty mold fungi that develop on honeydew cause the fruit to turn black, reducing its quality.

GREEN APHID TERMINAL DAMAGE

Aphids should be sampled several times throughout the season starting in June. Inspect 10 rapidly growing terminals from each of 5 trees throughout the orchard. Record the percentage of infested terminals. No formal studies have been done to develop an economic threshold for aphids in N.Y. orchards. Currently, treatment is recommended if 30% of the terminals are infested with either species of aphid, or at 50% terminal infestation and less than 20% of the terminals with predators. An alternative threshold is given as 10% of the fruits exhibiting either aphids or honeydew.

The larvae of syrphid (hoverflies) and cecidomyiid flies (midges) prey on aphids throughout the summer. These predators complete about three generations during the summer. Most insecticides are somewhat toxic to these two predators, and they usually cannot build up sufficient numbers to control aphids adequately in regularly sprayed orchards. Check Tables 5 (p. 45) and 12 (p. 52) in the Recommends for toxicity ratings of common spray materials. Both aphids are resistant to most organophosphates, but materials in other chemical classes control these pests effectively, including Asana, Danitol, Dimethoate, Lannate, Provado, Thiodan, and Vydate.

Woolly apple aphid (WAA), Eriosoma lanigerum (Hausmann)

WAA colonizes both aboveground parts of the apple tree and the roots and commonly overwinters on the roots. In the spring, nymphs crawl up on apple trees from the roots to initiate aerial colonies. Most nymphs are born alive to unmated females on apple trees during the summer. Colonies initially build up on the inside of the canopy on sites such as wounds or pruning scars and later become numerous in the outer portion of the tree canopy, usually during late July to early August.

Aerial colony of wingless adult female woolly apple aphids

Aerial colonies occur most frequently on succulent tissue such as the current season's growth, water sprouts, unhealed pruning wounds, or cankers. Heavy infestations cause honeydew and sooty mold on the fruit and galls on the plant parts. Severe root infestations can stunt or kill young trees but usually do not damage mature trees. Large numbers of colonies on trees may leave sooty mold on the fruit, which annoys pickers because red sticky residues from crushed WAA colonies may accumulate on their hands and clothing.

During late May and June, water sprouts, pruning wounds, and scars on the inside of the tree canopy should be examined for WAA nymphs. During mid-July, new growth around the outside of the canopy should be examined for WAA colonies. No economic threshold has been determined for treatment of WAA.

Aphelinus mali, an encyrtid wasp that parasitizes woolly apple aphids

Aphelinus mali, a tiny wasp, frequently parasitizes WAA but is very susceptible to insecticides and thus does not provide adequate control in regularly sprayed commercial orchards. Different rootstocks vary in their susceptibility to WAA. The following resistant rootstocks are the only means of controlling underground infestations of WAA on apple roots: MM.106, MM.111, and Robusta.

WAA is difficult to control with insecticides because of its waxy outer covering and tendency to form dense colonies that are impenetrable to sprays. WAA is resistant to the commonly used organophosphates, but other insecticides are effective against WAA, including Thiodan and Diazinon.

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