After freezing temperatures in early April you may not need to thin very much. In the Magic Valley some orchardists are reporting as much as 90% kill on cherries and peach blooms. However apples and pears are better off.
Fruit trees often set more fruit than they can support or develop properly. This is increasingly a problem on trees that have not been properly pruned. Excessive fruit compete with each other for the limited stored energy in the plant. This keeps most of the fruit a smaller, unmarketable size. This depletion process in one season can create devastating ‘June drop’ the following season and begin an alternating bearing cycle. Thinning fruit each year in the spring and proper pruning each winter helps prevent these problems from developing.
Thinning fruit when it is young allows each remaining fruit to develop to its maximum size, without reducing the trees vigor. Less crowded fruit receives more sunlight, so fruit color and flavor may be enhanced.
Fruit should be thinned when they are relatively small. Typically stone fruit are thinned when they are ¾ to 1 inch in diameter. Apples and pears are thinned at ½ to 1 inch or within 30 days after full bloom. Thinning to early can result in split pits in stone fruit. Whereas, thinning late will reduce the chances that fruit size will increase.
Small fruiting varieties of apricots and plums can be thinned to 2 to 4 inches apart on a branch. Larger fruit like peaches should be pruned to 3to 6 inches apart. If the load is light due to the natural thinning of the frosts, less thinning is required because the total number of fruit is low.
Apples and Pears produce clusters of fruit from the flower clusters. These clusters should be thinned to not more than one to two fruit per cluster, depending on the total fruit set and growing conditions. Retain the largest fruit normally developing from the King bloom or first bloom to open. If the crop is heavy, fruit should be spaced no less than 6-8 inches apart.
Hand-thinning involves removing enough fruit to leave the remaining fruit with sufficient space to they do not touch at maturity. On short spurs, this may mean leaving only two or three fruit per spur. Smaller branches should be thinned more heavily to reduce the chance of breakage.
Chemical-thinning is effective for large commercial operations or when hand thinning is not feasible. Usually homeowners are not happy with chemical-thinning because results are variable and a slight overdose can result in complete fruit removal and leaf drop. An inadequate dose wastes time, money, and the opportunity to maximize fruit growth.
Ethephon, 6BA(cytokinin), Amid-Thin W(NAD or NAAm), NAA (napthaleneacetic acid), and Cararyl (Sevin) are chemical thinning products. Read and Follow label instructions carefully.
Hand thinning will take time and effort, but the improved fruit quality and consistent cropping will be worth the effort. Here are some factors to tips to consider:
Use chemical thinners only in blocks where bloom density and pollination were adequate to set an excessive crop.
Sunny weather: harder to thin. Heavy clouds for 2 to 3 days: easy to thin.
Cool weather (below 65°F): less thinning. Hot weather (above 80°F): more thinning.
“2X4”—The temperatures and sunlight on the 2 days before, and the 4 days following thinner spray are the most critical.
6BA (MaxCel, Excelis Plus) is not very effective when the temperature is below 68°F.
Carbamates (Sevin and Vydate) are still somewhat effective in suboptimal temperatures.
All thinners work best when temperatures are in the 70s, and all chemistries have the potential to overthin when temperatures are in the mid- to high 80s. There is no “safe” thinner at high temperatures.
Adding carbaryl in a tank mix with NAA or 6BA increases thinning response. Adding oil at 1 quart per 100 gallons of finished spray mix boosts efficacy of all thinners.
Varieties once considered chemically hard to thin (Golden Delicious, Gala, Fuji) may not be hard to thin with a 6BA/ carbaryl tank mix.
For most effective thinning, no less than 100 gallons of water per acre should be used for adequate coverage, and sufficient wetting time must be allowed to permit foliage to absorb the thinner.
Use extra caution if freezing temperatures occurred during bloom. Delay thinning until you are certain that fruits are growing. Consider reduced rates of chemical thinner in this circumstance.
Trees less than 5 years old are more apt to be overthinned.
In some instances, it may be desirable to remove all fruit from the trees. In such cases, a mixture of 15 ppm NAA, 2 pints of Sevin XLR, and 1 pint of spray oil per 100 gallons of water applied at petal fall is effective.
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