Effects of Managing Citrus Red Mite (Acari: Tetranychidae) and Cultural Practices on Total Yield, Fruit Size, and Crop Value of 'Navel' Orange

Abstract

The value of suppressing spring populations of the citrus red mite, Panonychus citn McGregor, at or below the conventional treatment threshold of two adult females per leaf was determined on ‘Navel’ orange, Citrus sinensis (L.) Osbeck, in the San Joaquin Valley. Mites on untreated trees reached peak populations between five and eight adult females per leaf. These higher mite populations caused significant reductions (∼10%) in yield in only one of three studies. Average fruit size per tree increased with increasing mite-days in all three studies. Fertilization level was the only cultural practice to consistently affect total fruit yield, and yield increased with increasing fertilization level. Increasing irrigation levels also increased fruit size. The rate of fruit ripening was accelerated with increasing fertilization level and delayed by the application of a growth regulator to delay rind senescence. In general, total yield per tree and average fruit size did not differ significantly due to interactions between acaricide treatments and the 36 other combinations of cultural practices. On average, large fruit are more valuable than small fruit, although there is substantial variation in price structure among seasons. Therefore, the slight increases in average fruit size on acaricide-untreated trees compensated economically for slight reductions in total yield. The economic benefit of suppressing citrus red mite populations in these studies depended greatly upon the price structure in effect when the crop was harvested and sold 7-11 mo after treatment decisions had to be made. Often, the increase in crop value did not offset the cost of acaricide application.