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Healthy Fruit 1997 Vol. 5:3

Apr 23, 1997

Growth Stage. . . Are We Having Spring Yet?

McIntosh moving into 1/2 in green in most areas, and even some tight cluster will show by the end of the week in early areas.

Scab Outlook

The next wetting period will probably be a big infection period, if the rain lasts long enough. Either be protected, or plan to treat with an SI (Nova or Rubigan) after the rain.

Tarnished Plant Bug

In most orchards where white sticky rectangle traps are in place, captures remain below a level that would warrant consideration for treatment. In general, TPB adults do not become highly active until the temperature rises above 70F, which has not yet occurred. In one early orchard, a treatment of dimethoate was applied at 1/2" green, which is the latest stage of tree development at which we recommend applying this material. The thresholds at which treatment should be considered are given as follows in the 1997 March Message:

If insecticidal control is necessary, Guthion, Imidan, and Lorsban remain the pesticides of choice. Pyrethroids (Asana, Ambush, Pounce) are usually more effective than Guthion, Imidan, or Lorsban and are cheaper to buy, but often prove more expensive in the long run because of the negative effects on predatory mites. Growers who are considering using a synthetic pyrethroid against tarnished plant bug or leafminer should be aware of the devastating long-term effects which these materials have on predatory mite populations.

In a 1996 study in California, it was found that 7 months after a single pre-bloom application of synthetic pyrethroid, enough residue remained on the bark (a favorite resting place of predatory mites) to kill 50% of the predators.

Leafminer Activity

In most orchards monitored with sticky red rectangle trunk traps, cumulative trap captures remain at 0-2 leafminers per trap.

However, in one orchard trap captures have exceeded 20 leafminers per trap, signifying a high population in need of treatment. Captures on trunk traps remain as the best existing way for determining the need for pre-bloom or petal fall sprays against LM. Based upon our most recent information, we suggest the following:

Materials labeled for use against leafminer include Vydate (no later than early pink) and synthetic pyrethroids (Asana, Ambush, Pounce) from pink until late pink. We do not recommend use of either of these chemicals due to their negative effect on predatory mite populations. Alternative chemicals which fit within an IPM approach to orchard management include Provado (no later than petal fall) and Agrimek at petal fall or within one week thereafter. Both Provado and Agrimek are safe on mite predators. Experience in Massachusetts in 1996 indicated that a Provado application at petal fall was much more effective against first generation leafminers than a late June spray of Provado against the second generation.

Mite Bite

The recent registration of 3 new miticides (Apollo, Savey and Agrimek) and the recent loss of Omite as a summer rescue miticide has substantially altered approaches to mite management. The challenge now is to effectively weave together all of the following considerations when choosing a management approach: size of overwintering European red mite egg population; types of insecticides and fungicides to be used and their probable effects on mite predators; and comparative cost of materials.

Predators ought to be the foundation upon which all other mite management tactics are built. In New England, we have at present only one truly effective mite predator, Amblyseius fallacis, that is widespread throughout the region. Unfortunately, cold weather during winter usually takes a heavy toll on A. fallacis, reducing it to low numbers by spring. Rarely does it build sufficiently to provide effective biocontrol until late July. But in orchards not receiving

predator-harmful insecticides or fungicides, A.fallacis often controls mites well from mid-summer onward. At present, only a few New England orchards are blessed with detectable numbers of the predator Typhlodromus pyri, which is capable of providing excellent season-long biocontrol of mites, even during spring and early summer. Some orchards in every New England state are currently being seeded with T. pyri. But until T. pyri becomes widespread, growers will have to rely on some form of pesticide application (even if just oil) to prevent pest mites from reaching damaging numbers before A. fallacis appears.

The most recent information from research conducted in the Northeast suggests that one or more of the following pesticidal approaches ought to give effective mite control at least through mid-July (and possibly longer) in orchards having insufficient numbers of T. pyri predators: application of Apollo (1.3 oz/100 gal. or 4 oz/acre) in combination with oil (1 gal/100 gal or 3 gal/acre) at tight cluster or early pink; application of Savey (1 oz/100 gal or 3 oz/acre) in combination with oil (1 gal/100 gal or 3 gal/acre) at tight cluster or early pink; or application of Agrimek (3.3 oz/100 gal or 10 oz/acre) in combination with horticultural spray oil (3 pints/100 gal or 1 gal/acre) at petal fall. The per acre cost of Apollo and Savey is virtually identical, whereas the per acre cost of Agrimek is about 40% greater; but Agrimek controls leafminers as well as mites. All 3 of these pesticidal approaches appear to be about equal to one another in effectiveness against European red mites and two-spotted spider mites, but none of them appears to be effective against apple rust mites.

Apollo and Savey have very similar modes of action and should therefore be considered interchangeable with each other in terms of resistance management. In several countries, resistance has begun to appear to each after only 5 or 6 consecutive years of 1 application per year. Therefore, it is highly recommended that growers alternate Apollo or Savey with Agrimek on an every other year basis if these materials are to be used.

Comparison can be made between use of Apollo, Savey or Agrimek in combination with oil versus oil alone for mite control. Several years of research suggest that 2 gal/100 of oil alone at half inch green followed by 1 gal/100 of oil alone at tight cluster or early pink usually suppresses mites effectively until late June or early July, providing 3 or 4 weeks less residual effectiveness than oil combined with Apollo, Savey or Agrimek. Application of 2 gal/100 of oil at half inch green followed by oil in combination with Apollo or Savey at tight cluster or early pink or Agrimek at petal fall aids in mite control where overwintering eggs of European red mites are abundant and aids in control of San Jose scale. But this approach appears to provide little added benefit where overwintering eggs of European red mites are moderate or few. Like Apollo, Savey and Agrimek, oil is safe on beneficials.

The cost of a pre-bloom double oil program is about 40% less than the cost of Apollo, Savey or Agrimek in combination with oil.

Ideally, a decision on whether or not to apply Apollo, Savey or Agrimek ought to be made in conjunction with sampling information on the population size of motile mites on foliage. Recent research suggests, however, that it is very difficult to obtain a reliable estimate of mite populations when they average fewer than 1 per leaf at pink, bloom or petal fall. Populations reaching or exceeding 1 per leaf merit strong consideration for treatment with Apollo, Savey or Agrimek in combination with oil. Lesser populations may or may not merit such treatment.

Pear Thrips/Pear Psylla

According to observers of maple trees, pear thrips are not abundant as yet this season. This would perhaps suggest that we will escape their potentially harmful effects this year.

Psylla flight and egglaying activity continues this week. Most orchards have oiled once so far, so egg deposition is light to moderate.