Producing the largest prunes possible

With a current Prune Board estimate of 160,000 tons, an estimated carryover of 40,000 tons and a large supply of prunes in South America (120,000 tons), many of them small — it is easy to see that there will be no money in producing small prunes.

Sunsweet has informed it’s growers that it will not pay for D size or smaller (96 count per pound or smaller) prunes. Delivering prunes of this size or smaller will have no value, but will incur hauling and drying costs and industry assessments. What can be done at this point to get the best out of what you have?

Management considerations:

• Nutrition:

Make sure that your crop is adequately supplied with potassium (K). Heavy crops can draw down potassium levels rapidly. Leaf levels have been observed to go from 1.6 per cent K in July to 1.0 by early August under heavy cropped conditions. If the crop runs short of K before the prunes are ready to harvest dry size could be reduced. Foliar potassium sprays can be applied through July and are advisable on heavily cropped trees with marginal K levels.

• Irrigation:

Make sure your orchard is well irrigated during July. Water stress before fruit maturity can adversely affect fruit sizing. While it may not increase sizing potential, mild to moderate levels of water stress near harvest in August can help achieve desirable sugar content in fruit and reduce “dry-away” (drying costs). Developing moderate stress shortly before harvest may improve drying ratio by beginning the drying process on the tree.

• Harvest timing:

Ideally prunes are harvested when soluble solids reach 24 percent and fruit pressure drops to 3-4 pounds.

Green tonnage peaks at this point and begins to decline as fruit drop increases. Dry tonnage decreases to a lesser degree because it is partially offset by an improved drying ratio. Harvest costs are reduced with later harvest due to reduced green tonnage (assuming costs are per green ton and not per acre or per tree). Blocks with light crops may achieve good soluble solids while fruit is still greater than four pounds pressure and are good candidates for earlier harvest. Blocks with heavy crops will generally have better returns when harvest is later than normal. Risks of later harvest include weather events, such as high winds, which can increase drop, potential increased losses if brown rot is developing in the orchard, and limited harvester and dryer capacities which can further delay harvest.

• Sizing at harvest:

Harvest sizing is a last resort for improving fruit size in your crop. Given the current crop and market conditions growers with large crops of small fruit should consider this option to help reduce harvest cost and improve the value of the remaining fruit. This can also help the industry improve the ability to market the 2010 crop by reducing the carryover and especially the supply of smaller less marketable fruit.

Points to consider with chain sizing:

• Sugar and pressure:

Fruit with higher soluble solids will have a better drying ratio and result in larger fruit. As the season progresses fruit softens and continues to accumulate sugar so the opening on the sizer may need to be adjusted to avoid removing fruit with value.

• Keep sizers clean for proper functioning.

• Don’t overload sizers. It may be necessary to reduce harvest speed for sizers to function properly.

• Monitor discarded fruit by checking soluble solids and fruit sizes of dropped fruit or by drying and analyzing a sample to be sure that you are removing what you want to.

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