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As I See It: Cold Injury, Fireblight and Apple Thinning

by Win Cowgill, Professor and Area Fruit Agent

This has been a tough spring to figure out what to do next. You can see by the title of this article there are a number of issues to deal with for the next few days. My trees have virtually stood still for the past five days. I had first bloom on apple at Rutgers Snyder Farm on April 11. It's been a long draw out bloom and of most concern is that every tree I have still has open bloom and some pink clusters, mostly on one year wood, but they are there none the less.

With the warming trend the next few days and mid 80’s forecast for Friday and showers every day we are most concerned with Fireblight. NEWA is forecasting a Caution warning today (Tuesday) and Wednesday Extreme risk for Thursday, Friday, and high risk for Saturday.

Fireblight Sprays- our choices are Fire Blight are Streptomycin as Agrimycin or Firewall or Oxytetracycline as Fireline or Mycoshield, I will be spraying my apples at Snyder Farm Wednesday am, May 2, 2012.

Also if you are using Apogee for the shoot blight phase, you should have had the first application on several weeks ago. I am making my second 4 ounce application tomorrow. If your looking to increase set in frost damaged blocks you can increase the rate to 6 ounces.

Apple Scab is still of concern as well with this additional wetting for next three days. Make sure you are covered with protectants as you spray for fireblight, i.e. captan or mancoczeb. If using Regulade with the strep do not add captan, use a mancoceb product instead.

Apple Thinning: Every one is asking what do we do now? We are at a difficult juncture. The fist thing is make sure you know what you crop set is and your crop load. In many cases it may still be difficult to assess that. Some fruitlets are growing slow or not at all. With the warm weather Friday we should move rapidly and be able to see things better.

We are definitely at or past petal fall in North Jersey on most varieties on the spur fruits, with many clusters at 8mm or larger.

Note, with most trees having some bloom on one year wood we are not at full PF so be careful of any insecticide including Sevin so as not to kill bees. If you know what you have and had great pollination, and fruit is staying, consider still being conservative but get some Sevin XLR on now. Spray in the evening after bee activity has stopped to avoid bee kill. The XLF formulation is better on bees than the WP formulations. I have always advocated a PF spray, and put Sevin XLR on most of my cultivars last Wednesday night. The downside to that early application is that it takes 6-9 days to see where we are. I would get some thinner on now but be conservative if you have none on. Sevin XLR alone is the conservative approach.

Thinning Twilight – Phillips FARM this Thursday, May 3th , 6pm- see lst weeks plant and pest for details. We will go into greater detail then on thinning.

Cornell MaluSim Carbohydrate Model- Many of you know we are experimenting with this model with our NJ NEWA weather data to assist us in forecasting thinning response. We ran it today with the assistance of Rebecca Magron RCE and Jon Clements UMASS. It indicates that we should be conservative the next couple of days, as we know warm temperatures and cloudy weather make fruit easy to thin. Three days of cloudy weather will cause apples to thin. If you have questions call me.