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(Art Agnello ama4@cornell.edu, Entomology, Geneva)

We used to think that the popularity of petroleum oil as a delayed dormant application for mite and insect control was in decline in recent years, mainly because of the flush of effective early season miticides currently being developed and marketed for apples. However, horticultural mineral oils have been in use as crop protectants for over 100 years, and some traditions hold on for good reasons – for instance, oil is still relatively inexpensive, highly effective when applied properly, and virtually resistance-proof among the various tools we use against mites and psylla in N.Y. For these reasons, there is still justifiably wide use of oil during the early season in many growers' orchards, and the advice behind its use is still applicable, if familiar to many.

Pear Psylla

We weren't out there personally to witness it, but it's a pretty good bet that psylla adults have been active since the warm temperatures of early March, and have already started to lay eggs on those pear buds not yet covered by a protective oil spray.

Pear psylla adult

Pear psylla adults on pear leaf

Early oil applications can be very useful against pear psylla all through the swollen bud stage; although it's capable of killing adults and nymphs that are contacted directly, oil is used chiefly because the residue causes a reduction in egg-laying for an extended period after treatment. The strategy behind the use of oil is to delay the timing of any needed insecticide spray until as late as possible before (or after) bloom. Oil rates depend on when you start: If your buds are at the dormant stage, one spray of 3% oil, or two of 2% through green cluster are recommended; if you start at swollen bud, one spray at 2% or two at 1% up to white bud should be adequate for this purpose, especially if applied as soon as the psylla become active (50F or above). This will also give some red mite control at the same time.

European Red Mite

Despite the newly acquired prebloom miticides that are now available for apples, a delayed-dormant spray of petroleum oil from green tip through tight cluster can be a preferred approach for early season mite control, both to conserve the efficacy of and to help slow the development of resistance to our contact miticides. Technically, we have always advised that it is possible to get good control of overwintered eggs using 2 gal/100 at the green tip through half-inch green stage, or 1 gal/100 at tight cluster; this advice assumes ideal spraying conditions and thorough coverage. As we all know, oil applications don't always live up to our expectations, not only because of weather and coverage problems, but also because proper timing is difficult, especially if there are a number of blocks to cover during this transient window. That is, we have seen mites start to hatch when the trees are at solid tight cluster, so naturally the oil loses its ability to smother mites that are able to avoid (or trudge through) the droplets. For practicality's sake, there are a couple of guidelines to follow.

First, to ensure that mites are in the egg stage, start on your blocks as soon as the weather and ground conditions permit, even if this means using a higher rate. Fortunately, the low amount of snow and rain this winter has resulted in firmer orchard floors this spring, so although we may have to deal with droughty conditions later this season, you might as well take advantage of the positive side effects now by getting in some early sprays where possible. Also, tend toward the high end of the dosage range, especially if there's been no frost during the 48-hour period before your intended spray, and no danger of one for 24—48 hours afterwards. A compromise that might be worth making is to use 1.5 gal/100 if the buds linger somewhere between half-inch green and full tight cluster during your chosen spray period.

Good coverage of the trees is naturally critical if you're to take advantage of oil's potential efficiency; this in turn requires adequate spray volume delivered at an appropriate speed. Experience and research have shown that a 1X concentration (300 gal/A) in larger trees is clearly preferable; however, if all other conditions are optimal (weather, speed, calibration), then 3X, or 100 gal/A, is the highest concentration that should be expected to give acceptable control at any given time. Growers like to concentrate more than this to save time and the hauling of extra water, but the problems this can cause usually aren't worth the tradeoff.

Rosy & Jose

It was a common belief that San Jose Scale might actually be retired as a regular pest of N.Y. apples, but a small and determined group of populations scattered here and there refuses to be written off, and it's clear that they aren't gone yet (see following article). In this case, a 2% oil treatment at half-inch green will control the nymphs, and this is a preferred treatment if no other problem insects need to be controlled. Combining the oil with an insecticide has not been shown to be more effective than using the oil or insecticide alone. If you choose not to use oil against the scale nymphs, or if you have Rosy Apple Aphid or other early season insects to be controlled, an insecticide would be more appropriate. For both of these pests, Lorsban 4EC or Supracide (2EC or 25WP) have proven very effective during the green tip to tight cluster stage. Check the opening buds for infestations of Rosy Apple Aphid; treatment would be advisable upon finding one colony per 100 clusters.

(Dick Straub dstraub@cce.cornell.edu, Entomology, Highland)

A number of growers throughout the state are experiencing a rebirth of problems with San Jose scale (SJS). This shouldn't be surprising, because the current luxury of having three efficacious postbloom miticides has resulted in the virtual abandonment of dormant oil sprays that formerly controlled or suppressed overwintered SJS populations in eastern N.Y. Although SJS may have three generations per season in warmer climes, N.Y. growers contend with only two generations. SJS overwinters on bark as 1st instar nymphs ('black-caps') and development resumes as temperatures exceed 10C (50F). Females do not deposit eggs, but rather produce live crawlers within 4—6 wk following mating – usually about 3 weeks after petal fall.

"Black-cap" form of third and (final) phase of first instar San Jose scale nymph

Infestation of the fruit induces local red to purple circular lesions around the sites of feeding. Growers that have an SJS problem will have noticed it sometime during late summer, or certainly at the packing line. Hopefully, the blocks from which the infested fruit originated were noted and the records kept for reference.

Red and purple discolorations marking San Jose scale feeding sites on fruit

Infestations tend to occur from a focus of a single tree, spreading to neighboring trees within the row. Spot treatments within and surrounding an infested area are often adequate to check this pest. If prebloom treatments (oil, Lorsban or Supracide) were not accomplished, three treatment scenarios utilizing either Lorsban or Provado may be used:

• Sprays against 2nd generation crawlers ~3 weeks after petal fall (500 DD [base 50F] accumulation starting 1 March), followed by another spray 7—10 d later. In heavily infested blocks, additional sprays may be necessary against 2nd generation crawlers at 1450 DD [base 50F] and 7—10 d later.

• If pheromone-baited traps are used, the double spray scenario above should be used against each generation (310 DD after first male catch of 1st generation; and 400 DD after first male catch of 2nd generation).

• Crawlers may be monitored by affixing sticky tape around a number of randomly selected limbs throughout the block (suggested action threshold: 1—2 crawlers/trap).

Obviously, each scenario has windows within which SJS will be impacted by treatments for other pests - Provado and Lorsban are often applied for other insects such as leahoppers, aphids, leafminers or leafrollers. In such cases, specific sprays for SJS may not be necessary during each generation of this pest.

end of this issue

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