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Healthy Fruit 1997 Vol. 5:7

May 21, 1997

Apple Development

In the earlier-developing areas of the state, McIntosh development ranges from late bloom to early petal fall. In the later-developing areas, trees are for the most part at mid- to late pink.

Leafminer Still Going

In some areas, leafminer captures are continuing to build even at this late date, which is reflective of a large overall population statewide. Egg densities of 1-2 eggs per cluster have been seen in some monitored orchards, particularly those with high trap captures. As mentioned in previous issues of Healthy Fruit, the time to treat using either Provado or Agrimek is at petal fall or closely thereafter. This year, cool weather has prevailed and the development of LM eggs and larvae can be expected to be slower. Because of this, orchards which have exceeded treatment thresholds on LM traps can delay the post-bloom application against LM to several days after petal fall with little risk.

See Sawfly With Warmer Weather

The weather over the past week (during late pink and into bloom in most orchards) has not been conducive to sawfly activity, nor has it been conducive to EAS trap captures in potentially infested orchards. Some blocks in some orchards have definitely exceeded trap capture thresholds; in these areas consideration of a treatment at petal fall or soon after is warranted. However, most orchards have not approached thresholds for treatment, which either means that the populations are low in these areas or that the weather has yet to trigger a level of activity which is indicative of the actual population density. In most areas this year, the weather has simply been too cool to give an accurate indication of the population present in the orchards.

Curculio Lurking

In some monitored orchards, plum curculio adults were caught in black pyramid traps next to the tree trunks. The moderate temperatures on Monday, coupled with the damp conditions, allowed PC adults to crawl into traps next to the tree trunks, the first captures of this season. So far, no PC feeding or egglaying has been observed even on wild plums, which generally harbor large populations of PC and are currently at the stage of development when PC injury is most likely to begin. No PC have yet been observed from tapping over groundcloths either, which tells us that while the weather has allowed the PC to arrive at or near the bases of orchard trees, it has not yet allowed movement into the canopies.

As mentioned earlier, the cool weather has delayed the development and activity of both sawfly and leafminer larvae. Because of this, growers may be wise to withhold the petal fall PC treatment until the weather is warmer and there are signs of PC present in the tree canopies. This calls for a vigilant monitoring of traditional PC hotspots for indications of feeding and egglaying activity and taking action when the first signs are seen. If the orchard has little need for a petal fall treatment for leafminer, sawfly or plant bug, then a border row spray may be sufficient as the first PC treatment; waiting for warmer weather for a whole-orchard treatment against the invading population.

Mites In The Sites

In orchards where pre-bloom treatments were less than optimal, a fair number of motile nymphs and some adults have been seen. Refer to last week's Healthy Fruit or the 1997 March Message for sampling and treatment recommendations.

Travels With Gypsy Moth

In a few orchards, early instar gypsy moth have been seen on trees bordering stands of oak. While we do not expect a big year for gypsy moth, there could be a few local trouble spots. If this is the case, growers should be concerned with young trees which received no pre-bloom insecticide treatments and are adjacent to stands of oak. Large numbers of young larvae, which blow into the apple tree canopies from adjacent oak trees, can cause significant damage to young trees, stunting their development.

Pear Psylla, Be Warned

Petal fall is the time to begin thinking seriously about options for insecticide applications against pear psylla. According to research done in New York state, Agrimek in conjunction with horticultural spray oil applied 1-2 weeks after petal fall provides 4-6 weeks of protection under normal conditions. If the material of choice is Mitac, back-to-back sprays are recommended, with the first occurring 2 weeks after petal fall and the second 7-10 days later.

To reiterate, if Agrimek is used, it should be applied with 1 gallon of horticultural (not dormant) oil per acre. Agrimek is not effective unless it is used in conjunction with a material which facilitates penetration into the leaf tissue. Up until now, horticultural oil has been the recommended material to aid in penetration, but the manufacturer of Agrimek has indicated that it may work as well in conjunction with a penetration facilitator other than horticultural oil. This would alleviate the compatibility problems encountered in an orhard management program which includes Captan or sulfur. At present, the manufacturer is not recommending any specific alternatives to horticultural oil, but materials such as Sil-Wet may become an alternative.

Scab Infections Continue

Of course, weather can never be windy and dry, or wet with calm intervals. In New England, it has to be windy and wet, making it nearly impossible to spray, but keeping the primary scab season filled with infection periods. Fortunately, among us we have observed only one commercial orchard with any signs of apple scab. We have not quite accumulated enough degree days to call primary season done and over, but may, with any warm weather, be there by the middle of next week. At that time, we will provide an update on treatment.

Fire Blight Infections Unlikely

With most of Massachusetts McIntosh in some phase of bloom, a check of the MaryBlyt model shows that the risk of infection is very low. It's been too cold, as if you didn't know. However, a prolonged bloom and some warm weather may tip the balance to cause problems on late-blooming varieties in some areas by the end of the bloom period.