May 3, 1999

L.P.Berkett, IPM Specialist

Stage of Development:

With the warm temperatures predicted for most of this week, bud development will progress rather quickly.

Apple Scab -- The following chart contains the estimated DD accumulated as of 5/02/99.

You can see that we are headed into the "accelerated phase" of ascospore maturity which extends from 300-700 DD. Now is the time of HIGH RISK because there is more susceptible tissue out there and the percentage of the season's ascospores that are matured and ready for discharge builds up rapidly. We will have reached 20% mature at the warmest sites over the next day or so.

So far, with the dry weather, there have been very few potential "infection periods" and, in some locations in the state, there have been no infection periods to date. Some growers may even enter bloom without having applied a fungicide yet. But, BEWARE ! Make sure your trees are covered if the weather turns wet. [Also, see note below about Powdery Mildew.]

The question has arisen: "Has the dry weather affected ascospore maturation in the leaf litter?" I suspect the very dry weather has negatively impacted ascospore development in the leaf litter but it is an impact that cannot be measured. So bottom line, if you went into the winter with high levels of foliar scab on the leaf litter, continue to assume your ascospore potential is high.

Powdery Mildew -- Note that dry conditions and warm temperatures are favorable for powdery mildew development. If you have cultivars that are highly susceptible to this disease such as Ginger Gold, Cortland, Gala, Paulared, Idared, Rome Beauty, Granny Smith or Jonathan, please refer to the March issue of the Vermont Apple Newsletter for disease management information.

Arthropod Management Update

Based on estimated DD, Leafminers and Tarnished Plant Bugs should be active. ERM egg hatch is estimated to begin at approximately 100 DD. Oil application for ERM management is still an option for many orchards in Vermont but it should not be applied past tight pink.

This past week we literally caught thousands of LM moths in our pheromone traps at the Hort.Res.Center. However, we suspect most of what we caught were adult Lyonetia Leafminers and not the spotted tentiform or apple blotch leafminer. The Lyonetia Leafminer, also called the Apple Leafminer, has been building up in numbers in our orchard and in orchards around the Northeast. It is a moth whose larvae produces the following type of mine:

[Picture from: "Apple Leafminer" by Dick Staub, Scaffolds, Vol. 7, July 1998]

If leaf mines develop in your orchard (which hopefully, they will not !) look closely at them to see if they are this type of mine.

Early Pink     Place EAS traps in orchard

Late Pink     Check TPB and LM Red Sticky Traps to determine if thresholds have

been reached

Bloom    Place CM pheromone traps in orchard

                    Begin to inspect fruit for PC injury during late bloom

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