A Speck on the Horizon
It has been a dry year, in terms of precipitation. Last week, we pointed out that "for the flyspeck fungus, ... very high humidity is just about as good as wet weather". And in case anyone hasn't noticed, it has been humid. Right on cue, Heather Faubert, IPM specialist at URI, called and said that a block of scab-resistant cultivars that had not received fungicides were showing the first signs of flyspeck.
This block is relatively near the coast, in Kingston, RI, and is subject to fog and other high humidity phenomena. While they haven't gotten any more precipitation than the rest of the region, the humidity has been sufficient to grow flyspeck.
Low rates of fungicide should be sufficient to stop flyspeck. The point of this cautionary tale is to warn people to put on a that low rate of fungicide, and not forget it completely, unless you have customers who won't mind a little flyspeck come September.
Fly Low
As was the case with plum curculio, this season's apple maggot population is shaping up as one of the lightest in recent memory. Captures on unbaited monitoring traps have moved little in the last week; the statewide average remains at or slightly below treatment threshold (2 AMF per trap), and only a handful of damaged fruit have been observed. Only a few sites are exhibiting signs of a substantial threat of AMF infestation, most notably an early-ripening block with captures up to 50 AMF per trap.
Most growers applied either Imidan or Guthion earlier this month to control the early side of AMF invasion. Many have seen the interval since the first treatment grow to 3 weeks or more, with too little accumulation of AMF on monitoring spheres to trigger a second application. In some cases, a second treatment may not be necessary until August—in others, it may not be necessary at all. However, the threat of additional AMF invasion has not passed, as immigration and activity generally extends well into August.
As mentioned in earlier issues of Healthy Fruit, a season of light pressure can add to the value of using traps to monitor the abundance of AMF. In a season such as this, growers may see a direct financial return from extending the interval between applications or reducing rates in response to lighter populations. In addition, regular monitoring of traps may alert growers to later-season invasion and buildup of AMF, which is still a distinct possibility this year. Due to the uncertainty surrounding continued use of Guthion on apples, growers may opt for use of Imidan, and reduced rates should handle the AMF threat in most orchards.
Testing Their Mite
European red mite populations are very low in most monitored orchards, and nearly all blocks receiving either a full oil program or an early-season miticide remain free of mite stress. As mentioned last week, a few growers found it necessary to spot-treat (generally using Pyramite), and most areas of concern have cleared up nicely. We have no sure-fire explanation for the lag in mite population growth, although under humid conditions, mites do not generally flourish, likely due to the impact of fungal pathogens.
Monitoring the buildup of mites (particularly on susceptible cultivars) through the first half of August can still be beneficial, allowing growers to manage an impending threat before the damage is irreversible. At this stage of the season, treatment is recommended if 80% or more of middle-aged leaves (taken throughout the canopy) are found infested with motile mites. If treatment is necessary, Pyramite remains as the material of choice.
Generation Gap
Neither leafminers nor leafhoppers have mustered much threat of late, largely due to the profound impact of Provado in June. Some second-generation LM have begun to pupate (though sap-feeding mines are still present as well), and substantial rates of parasitism have been observed. In all, the massive LM trap captures early in the year have not amounted to much, which hopefully will carry through the season.
Any growers who are currently noticing high populations of leafhoppers should be aware that the population may well be intolerable by harvest. If the leafhopper load is considered excessive, a low rate of Provado (1 oz./100 gal.), a half-rate of Thiodan, or a treatment with Sevin should take care of the harvest nuisance.
New Kids on the Block
In the past several years in New York and Massachusetts, orchards have begun to see moderate infestations of a third species of leafminer, the apple leafminer. The following is taken from the 1998 March Message, condensed from "Scaffolds".
Unlike the mines of spotted tentiform leafminer and apple blotch leafminer, which have a perforated appearance, mines of the apple leafminer appear as brown blotches. Also, ALM constantly expels excrement on a silken thread from the mine, which ABLM and STLM do not do. Finally, just before pupating, ALM larvae spin cocoons which are suspended by threads and resemble a hammock. ALM has 4 to 6 generations per year in the Hudson Valley, whereas ABLM and STLM generally only have 3 per year. Of particular importance is the fact that larval damage of ALM is confined to the youngest foliage, especially terminal leaves of vigorously growing shoots and watersprouts. Severely damaged leaves tend to drop off prematurely, thereby decreasing the number of the most photosynthetically capable leaves.
The potential for economic injury is greatest in young blocks, which can ill afford to suffer reduced photosynthesis. Infestations of ALM are most apparent toward harvest, but fortunately, such infestations are not known to cause premature fruit drop. ALM do not seem to be controlled by organophosphate insecticides, but apparently are susceptible to the same materials effective against ABLM and STLM. Sprays against ALM may be needed only on non-bearing trees where vigor is essential or on bearing trees that had a high infestation the previous year.
Free Bird
Unusually high levels of bird damage have been observed in some orchards, owing to substantial spells without rainfall. Early-reddening varieties such as Cortland are notoriously susceptible to bird damage, as are most peaches, and growers may benefit from use of deterrents in these blocks. Scare-Eye balloons are the most commonly-used bird control, and they are generally effective against flocking birds (crows, starlings, blackbirds). For maximum benefit, balloons should be placed at a 20-meter interval throughout the block, on poles that suspend the balloon roughly 1 meter above the canopy. Balloons are available from most orchard supply vendors, including OESCO (Massachusetts), Great Lakes IPM (Wisconsin), and Gempler's (Michigan).
The Beetles
At this time of year, it is not unusual to see substantial buildup of Japanese beetles in orchards, feeding on foliage. Like potato leafhopper and apple leafminer, damage from JB is most alarming on young, nonbearing trees, and is generally of little concern on mature plantings. If JB build to unacceptable levels (particularly on young trees), a treatment of Sevin should offer good control, while allowing a short pre-harvest interval.
Predicting McIntosh Size
In general, the growth rate of apples is relatively stable, so it is possible to predict average final fruit size based on average size at various times during the summer. Obviously, this prediction can be affected by severe drought or stresses that cause significant leaf damage, but it can be used as a rough estimate. To sample size, measure the diameter of at least 25 fruit within a block of trees of similar rootstock, age, and condition. Compare the average of those 25 numbers to the chart below. For example, fruit that average 2.4 inches in diameter on August 1, likely will average near 3.1 inches on September 16. Fruit that are 2.4 inches on August 15, on the other hand, likely will average only 2.8 inches on September 16.
