Ak Your PCA: What applications are recommended in the fall for citrus?

By Chris Boisseranc
Southwest Ag Consulting Inc., Redlands

Plant growth regulators are applied to navel oranges in October. Gibberellic acid is used to slow the development of the fruit and buy growers time so they can develop sales for niche markets.

All citrus fruits are sprayed with a copper mix. Sometimes it’s a copper sulfate and lime mixture such as Bordeaux. Many overseas countries require that citrus fruit be sprayed to prevent spreading diseases such as Septoria spot and Phytophthora. The applications help reduce disease in the export market, and it is required by packinghouses that export fruit to markets where there is a higher return. 

A side benefit of fungicidal applications is growers can add other treatments. In southern California, growers make applications for Asian citrus psyllid at the same time as fungicides. Copper can provide as much as 3 to 4 degrees of frost protection. 

Another plant growth regulator, 2,4-D isopropyl ester, is also applied, though it’s not the one used for weed control. 2,4-D strengthens the connection between the stem end and the fruit, and it can hold the fruit on the trees. 

This is important because navel oranges start harvesting in November and can go all the way to April or May, and Valencia oranges are harvested almost year-round. Holding the fruit until other countries leave the market allows U.S. growers to sell their crop when there’s less fruit on the market.

There is copper resistance, so it’s recommended to rotate chemistries. University of California farm advisers and export programs want growers to use the materials only one time, then rotate. 

Many growers prefer to use copper first for its frost protection benefits, which aren’t available with synthetic materials. Growers often apply the copper mix and plant growth regulators in November, and then if a second application is required due to persistent rains in January and February, they will use the synthetic materials. 

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