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Healthy Fruit 1997 Vol. 5:1

Apr 9, 1997

Growth Stage. . . Are We Having Spring Yet?

McIntosh at green tip in earliest areas, silver tip or dormant in later areas.

After surviving the April 1 blizzard, many of you will have noticed that it has been abnormally cold, with some areas experiencing 50 year lows or worse. However, the critical temperatures for apples and peaches were probably not reached. Check the latest Newsletter for details, but to refresh your memory, for our most advanced areas:

Apple at green tip: 90% kill at 10°F

10% kill at 18°F

Peaches,bud swell 90% kill at 1°F

10% kill at 18°F

In Amherst, the temperature was generally around 20°F at worst, though there may have been colder pockets. Check buds for browning.

Scab Spores

Looking at apple scab spore squashes over the last two weeks, it is apparent that there are plenty of spores available. Actual count in Amhest this week indicated 18% spore maturity. This probably overstates the real situation. However, growers should be aware that in high inoculum areas, there will beplenty of inoculum to present a problem when the first infection periods hit this year. The maturity is slightly advanced, and so orchards with low to normal scab levels should plan to apply scab fungicides at least as early as they normally do.

Oil Those Pear Trees Down, Boys

Adult psyllas were active in many pear blocks during the warm days of this past weekend but as yet there has been little or no egglaying.

Even though 3 effective materials are now available for use against psylla after petal fall (Agrimek, Provado and Mitac), the first line of defense should remain thorough coverage of pear trees with 2 pre­bloom oil sprays. If buds are dormant, apply a spray of 3% oil. If buds are swelling, use a spray of 2% oil. In either case, follow this up with a second treatment of 1% oil sometime between green cluster and early white bud (no later). Oil can deter egglaying as well as smother existent eggs, providing coverage is excellent.

Trap Tarnished Plant Bug

Silver tip is the time to hang white sticky rectangle traps for monitoring of tarnished plant bugs. Plant bug traps should be hung at knee height (no higher) at the tree periphery and attached to branch that will support the trap in the wind.

Trap Leafminers Too

Leafminer traps should be firmly stapled at knee height (no higher) to the south side of the tree trunk. For leafminer and plant bug traps, we recommend a minimum of 4 traps per 8­acre block.

Looking for Traps?

Both tarnished plant bug and leafminer are available through Gempler's of Wisconsin and OESCO (Orchard Equipment) of Conway, MA.

Which Fungicides Mite You Want to Use This Year?

A Chinese curse goes "May you live in interesting times." From the perspective of apple growers trying to manage scab, we certainly live in interesting times. Any fungicide program has potential problems, and finding the right answer on any farm still may leave one uneasy.

For example, as we gain more information on mite management, and developing biocontrol of mites, we seem to be cutting down fungicide options. Many of the best options for early­season scab control have been shown to be toxic to mite predators. Syllit (dodine) may be toxic to A. fallacis, while all of the mancozebs (Dithane, Penncozeb, Mancozeb) appear to be a problem on T. pyri. Polyram, another EBDC, may be somewhat less toxic to mite predators but to what extent or under what conditions this is true remains unclear. Benlate (benomyl) and its near relative Topsin M (thiophanate methyl) can also be harsh on A. fallacis. This leaves growers with essentially two options: captan and some type of SI, probably Rubigan or Nova. Captan is a problem for growers trying to use oil. We don't recommend using Rubigan or Nova alone. So what is there to use?

For those growers who have had successful mite biocontrol working for them, the answer is simple. If it ain't broke, don't fix it. There are growers using mancozeb who do have good mite biocontrol, and in those orchards, there's no reason to change.

For other growers, mite biocontrol may be relatively unimportant. Obviously, they don't need to worry about fungicides except in terms of cost and efficacy against scab and any other disease problems they may have.

There are probably a few growers who are actively working on promoting mite biocontrol. In these orchards, minimizing use of fungicides which are toxic to predators may be of value. If mites are a consistent problem, or if it has been impossible to eliminate miticides, making some adjustments to the fungicide program may be useful. In short, consider these points.

Use captan, or SI + captan for scab management.

If oil is used, probably the best selection, from the mite management point of view, is to use the highest label rate of the SI around the oil application (roughly a 7 day window either way).

Limit use of EBDCs, Syllit, benzimidazoles. Some use of these materials will probably present little risk to mites but be very beneficial in terms of disease managment.

Manage summer diseases with captan early, a benzimidazole + captan in late July or August.

Over the next few years, researchers should learn a great deal more about how to use fungicides in conjunction with mite biocontrol programs. Hopefully, this will make fungicide choices less interesting.