Scaffolds 99 index

NOBLESSE OBLIQUE

(Art Agnelloama4@nysaes.cornell.edu & Harvey Reissig whr1@nysaes.cornell.edu, Entomology, Geneva)

Moths of the obliquebanded leafroller have been flying in the Hudson Valley since and in western N.Y. since 6/2, which pretty much goes along with the trend of the current stretch of this season to be a bit ahead of normal. First hatch is generally assumed to occur about 360 DD (base 43°F) after the flight starts, and as of today our values stand at 129 for Highland and 115 for Geneva. This brings us quite naturally to the perennial question of how best to approach management of OBLR populations this year, so a brief synopsis of last year's research efficacy trials might be in order.

Pesticide control programs for the first summer brood of OBLR were conducted in two Orleans Co. orchards in 1998, one of them Idared trees and the other Romes. All sprays were applied using three or more of the following timings: Peak Flight (6/18), First Hatch (6/22), and "cover sprays" at various timings: 7/1, 7/8, 7/14, 7/21, 7/27—8

• Confirm was tested in six treatments -- 1: 3 sprays (6/18, 7/1, 7/14); 2: 3 sprays (6/22, 7/8, 7/27); 3: 3 sprays with DiPel (same timing as #1); 4: 3 sprays with the synergist Butacide, which contains piperonyl butoxide (same timing as #2); 5: 3 sprays with DEM, another synergist (same timing as #2); and 6: 6 sprays at 6 oz/A, which is 1/3 the recommended rate (weekly starting on 6/22 until 7/28).

• Intrepid, a "second generation" MAC (molting accelerating compound, the class to which Confirm belongs), was tested in two treatments: low (4 oz/A) and high (6 oz/A) rates in 3 sprays (6/22, 7/8, 7/27).

• SpinTor was compared in three treatments: low (5 oz/A) and high (7.5 oz/A) rates combined with the adjuvant LI-700 in 3 sprays (6/22, 7/8, 7/27); and 6 sprays at 4 oz/A (weekly starting on 6/22 until 7/28).

• Proclaim, an emamectin compound (related to abamectin/Agri-Mek) was tested in one treatment: 4.8 oz/A in 3 sprays (6/22, 7/8, 7/27).

• Rimon, a chitinase inhibitor (Dimilin was in this class), was tested in one treatment: 12 oz/A in 3 sprays (6/22, 7/8, 7/27).

• Lorsban 50W, Asana, and DiPel were applied as standard treatments using a 3-spray program (6/22, 7/8, 7/27).

OBLR infestations were considerably lighter in the Rome orchard than in the Idareds. None of the newer materials tested were any more effective in protecting fruit than were the standard materials, Lorsban, DiPel and Asana. The effectiveness of all schedules of Confirm in preventing fruit damage was fairly similar. The addition of DiPel, Butacide, or DEM did not increase the effectiveness of Confirm. The 3-spray program of Spintor at the highest rate (7.5 oz/A), and the weekly sprays of a low rate (4.0 oz/A) of this product were slightly more effective than was the 3-spray program using the 5.0 oz/A. The higher rate (6.0 oz/A) of Intrepid provided better control of fruit damage than did the lower rate. Treatments of Rimon significantly reduced fruit damage below that in the Check plots, but this material was not one of the most effective of those evaluated in these trials (fruit damage ranged from 5—10.5%, compared with 13.5—17.5% in the Checks).

Our recommendations for OBLR management this year follow along lines similar to those we have given previously. Most materials available should be at their maximum potential effectiveness when used 2—3 times (in moderate or high pressure orchards, respectively) against the first summer brood larvae. Applications in a 3-spray program should be made at times approximately corresponding to periods of first hatch, mid-hatch, and 2 weeks after mid-hatch.

Confirm is not available for use this year; although this material was granted a federal label, its application for a NYS registration is still under review by the DEC. Because of the availability of another comparably effective product (SpinTor), it was not possible to apply for a Section 18 emergency exemption again in 1999, so it will likely not be labeled for use in NY until next year. In orchards where SpinTor is being used, the suggested optimal treatment times are generally defined as 200—300, 500—600, and 800—900 DD (base 43°F) after first catch of the adults. The inclusion of a low rate of an adjuvant such as LI-700 or Sil-Wet is recommended. Because this material is reported to have fairly good effectiveness against larger larvae, and therefore could conceivably be satisfactory in a 2-spray program targeting the later instars, 1999 field trials are being conducted to test this approach. Increased efficacy with any of the B.t. products may be obtained by making more low-rate applications at shorter intervals (e.g., 4—5 sprays of DiPel at 0.5 lb/A, on a 1-week interval). As always, standard materials such as Lorsban, Asana, and Penncap-M are likely to work better against populations not having a history of extensive exposure to them.

BIOLOGY AND CONTROL OF SUMMER FOLIAR

AND TRUNK INSECT PESTS

(Dick Straub rws9@cornell.edu, Entomology, Highland)

Leafhoppers

In most of NY, white apple leafhopper (WALH), Typhlocyba pomaria, is a major foliar-feeding pest of apple. In eastern NY, rose leafhopper (RLH), Edwardsiana rosae, is also a major pest whose occurrence is correlated with the abundance of wild florabunda rose growing in close proximity to apple orchards. During their second generations, these two species occur simultaneously (Fig. 1), and thus generally make leafhoppers a more serious pest in the east. Leafhoppers are mesophyll feeders and damage is expressed as stippling or chlorosis of leaves, and the spotting of fruit by the excrement of nymphs and adults.

White mottling damage of apple leaves caused by white apple leafhopper feeding

Apple spotted by dried honeydew produced by white apple leafhopper feeding

The relationship of leafhopper damage to tree performance is controversial, but effects may be closely linked to the leaf:fruit ratio. In the past, management of leafhoppers has been accomplished by applications of methomyl (Lannate) or carbaryl (Sevin), materials that have been generally harmful to natural enemies. The recent registration of imidacloprid (Provado), which is essentially benign to natural enemies once it has dried, has provided an excellent tool for leafhopper control and integrated crop management. Generally, a single Provado treatment at 1st or 2nd Cover will provide season-long control of leafhoppers. Likewise, an application of Sevin (at the high rate) for thinning may provide season-long control.

Aphids

Two species of terminal-feeding aphids occur in NY - green apple aphid (GAA), Aphis pomi, and spirea aphid (SA), Aphis citricola. Both species occur simultaneously, and cause similar damage. Economic importance of these two aphids is due to: a) the stunting of shoot growth of non-bearing trees;

and b) direct feeding on fruitlets causing deformations,

or c) the secretion of 'honeydew' upon which sooty mold grows. Occasionally, infestations persist for the entire season, but during most seasons populations have collapsed by the end of June. This collapse is largely due to beneficial predator insects, primarily syrphids and cecidomyiids, that increase to efficient numbers during aphid outbreaks. These predators are generally resistant to most OP insecticides used during early season. If control is deemed necessary, Provado is excellent. A less costly alternative would be dimethoate.

Leafminers

Severe damage by leafminer (in NY, primarily spotted tentiform leafminer [STLM], Phyllonorycter blancardella) causes premature drop of fruit, reduced fruit set and reduced crop load on many cultivars grown in NY. The specific causes for leafminer-induced drop are unknown, but two popular theories include decreases in foliar magnesium, and enhanced ethylene production in leaves. We do know however, that leafminer can acutely alter the amount of photosynthetic tissue available (Table 1).

Table 1. Leaf tissue loss due to STLM. 1992

* (area of a penny = 3.5 cm²)

STLM in NY has three generations: the 1st affects spur leaves, while the 2nd and 3rd broods affect terminal and bourse leaves.

Tissue feeding mines caused by later spotted tentiform leafminer instars, visible from both sides of leaf

The last two generations can achieve high numbers (Fig. 2), and are often impacted by a host of predators and parasites. Third generation larvae are frequently heavily parasitized, reducing the proportion of overwintering pupae. Leafminers are generally resistant to organophosphate insecticides, but the carbamates Lannate and Vydate are effective. The recently registered 'soft' insecticides, such as Provado, SpinTor and Agri-Mek, have varying degrees of effectiveness against STLM.

Within the last decade, many Eastern NY orchards have become infested by apple leafminer (ALM), Lyonetia speculella. Adults begin emerging from overwintering pupae ~15 March, and ALM may have as many as seven generations per season (Fig. 3). Adults lay eggs almost exclusively on new growth, and are hence called terminal-feeders. During the latter generation (~10 July—15 Oct) the accumulated damage can be dramatic, and perhaps alarming to growers.

In young non-bearing plantings, in which rapid shoot elongation is important, terminal damage by ALM can be serious. In bearing trees, however, the precise effects on tree performance are unknown, but are considered to be of minimal seriousness. Because ALM has numerous generations, and because damage is limited to succulent tissue, the timing of insecticide treatments is difficult. Even the best leafminer insecticides may be ineffective in limiting damage.

Borers

In recent years, the incidence of infestations by dogwood borer (DWB), Synanthedon scitula, has become noticeably more prevalent. Infestations of this clearwing moth in apples are almost always located in burrknots or graft unions that are planted too high above ground level. Burrknots are aggregations of root initials that can develop on the above-ground portion of the rootstock; all commercial dwarfing and semi-dwarfing rootstocks have a tendency to develop burrknots. Some chemicals with hormone effects, such as NAA, can increase the expression of burrknots, as will failure to keep the area around the trunk weed-free and open to sunlight.

Burrknot tissue on clonal rootstock of apple, dogwood borer feeding sites

The adult seeks out these spots to lay eggs, particularly if they are surrounded by vegetation or protected by something, such as mouse guards. Moreover, mouse guards may frequently house weeds, and shield the lower trunk from incidental exposure to insecticide cover sprays. Sustained feeding by dogwood borer at the graft union may severely weaken the tree at this juncture, or girdle the trunk and cause a slow decline in tree health. Orchards in which mouse guards are emplaced should be examined for signs of damage.

Collections of frass produced by feeding of dogwood borer on burrknot surface

All grafted trees in NY should be periodically checked for infestation. White latex paint brushed on the exposed portion of the rootstock will prevent new infestations of the borers, and also protect against southwest injury to the bark. Dilute trunk applications of an insecticide with good residual activity can provide control of established infestations. Lorsban 50WP or Thiodan 50WP are the most effective materials if applied during the period between July 15 and August 15, bearing in mind the specific pre-harvest intervals.

Next in this issue: General Information