May 12, 2010
Hi Fruit growers,
This season continues to surprise and annoy. I heard of orchard temperatures down to 31 degrees yesterday morning, but I haven’t heard of lower temperatures in RI orchards. At the URI Agronomy Field House it was 29 yesterday morning. I do know that areas of NY and MA were in the mid to upper 20’s.

It takes 1-2 days for frost damage to show. Severe damage can be seen by cutting the fruit in half. Damaged fruit centers will be brown or water-soaked. Less severe damage is harder to spot – the fruit surface can be rusty either in patches or bands across or around the fruit.

Frost makes thinning even more difficult to decide what to do. At the bottom of this message is the UMass Healthy Fruit information from Duane Greene on thinning.

We are past Primary Apple Scab season in RI. It is still a good practice to keep trees protected with a fungicide for another week or so to protect fruit and foliage from any spores that may have developed in your orchard. After this time you can reduce rates and frequency of fungicide applications.

This cool (cold!) weather has halted plum curculio, though I finally saw two plum curculio scars today. According to Orchard Radar, we are only about 60% through the migration period for plum curculio. Early predictions are that your fruit needs to be protected with an insecticide through June 5. That’s still a long way off!

European red mites have not started to lay eggs yet, but Orchard Radar predicts that egglaying should start May 16 in Greenville and May 21 in Newport County. Ideally a miticide should be applied before this time if a miticide is needed (more than one mite per leaf or 30% of leaves with mites). Miticide choices include Savey/Onager, Apollo, Agri-Mek, Portal or Zeal.

Duane Greene thinning thoughts
Weather for the next 2 to 3 days is forecast to be very unfavorable for thinning. Even though fruit have grown into the size range where we normally consider applying thinning chemicals this is not the time to thin. Since developing fruit have not been stressed, the thinning window of opportunity has widened. At this point in time the weather starting this weekend and extending into next week looks favorable for thinners activity. While it is not necessary to have temperatures in the upper 60s and 70s to apply thinners, it is important that they be in place when the warm weather arrives. As it appears now our suggestions is to apply thinners later this week as long as wind and rain are not factors that will influence proper application and coverage.

All thinning chemicals are effective during the 8 to 14 mm stage of fruit development. Carbaryl is a relatively mild thinner. BA (MaxCel and other formulations) is a mild thinner when used by itself, however, when combined with carbaryl it is or can be a strong thinner. NAA used at low rates is not a strong thinner. Higher rates of NAA can cause strong thinning activity especially if temperatures in reach into the upper 70s after application.

The weather this spring, especially over the past 10 days, presents us with a thinning dilemma since damage may have occurred that is not apparent. There was a general and wide-spread frost last night. The good news is, if any, that you will have 2 to 3 days to assess any potential damage to fruit or foliage in advance of potential thinner application later in the week. If severely damaged, the center of developing fruit will be black. Look for darkened areas in a fruit that may signal damage but not death of a fruit. These fruit are vulnerable even to mild thinners so judgment must be exercised in what to do here. Foliage damage or foliage crinkling may seriously affect fruit set. If spur leaves are damaged, it is possible that fruit set will be reduced naturally and application of thinner or leaf-damaged trees may result in very heavy and inappropriate thinning.
Heather