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We have tried several approaches to mechanically thin peach, plum and nectarine flowers or fruit. These include trunk shakers to remove flowers or fruit and a drum shaker that has vibrating rods inserted into the canopy to remove developing fruit.
Generally, the earlier the thinning the better the improvement in fruit size and/or yield. Thus, we have demonstrated that blossom thinning can increase fruit value by as much as $2,000 per acre compared to fruitlet thinning (1997 KTFR Blossom Thinning Summary).
Peach trees are very sensitive to arsenic toxicity. The disorder has been found in several peach and nectarine orchards in the San Joaquin Valley. The toxicity is often caused by past use of arsenic based pesticides and herbicides, especially where grape vineyards were previously planted.
In 1999 we obtained 60 large (11' x 8' x 4' deep) plastic tanks and buried them in the ground at Kearney. We filled them with clean sand and planted a Zee Lady peach, Grand Pearl nectarine and Fortune plum in each.
Calcium deficiency has never been identified in California peach orchards. Most soils in the San Joaquin Valley are abundantly supplied with Ca and leaf samples generally show levels well above the deficiency threshold (1.0%).
Using Nemaguard seedlings growing in sand, we conducted a series of experiments comparing different zinc formulations. The seedlings were grown with a nutrient solution containing no zinc until deficiency symptoms were observed.
Zinc deficiency is common in peach, plum and nectarine orchards in the San Joaquin Valley. Generally, it is a rootstock problem as typical orchard soils are not deficient, but Nemaguard is a poor forager for this nutrient. Some other rootstocks do not exhibit the same problem.
We have several year's experience with a dormant season procedure for sampling shoots. There are still many details to work out, but it appears to show promise for some nutrients.
