Effect of citrus red mite (Acari: Tetranychidae) and cultural practices on total yield, fruit size, and crop value of 'navel' orange: years 3 and 4.

Direct and interacting effects of four seasons of uncontrolled citrus red mite, Panonychus citri (McGregor), populations with 36 other combinations of grove management practices were examined to seek the existence of long-term deleterious consequences of not controlling mite populations on Navel' orange, Citrus sinensis (L.) Osbeck. Results from the first 2 yr were published previously. In the 3rd and 4th yr, P. citri populations reached mean peak densities of 7.1 and 2.2 adult female P. citri per leaf at one site and 9.7 adult females per leaf at a second site on trees where effective acaricides were withheld. These populations caused yield reductions of 9, 6.6, and 11.4%, respectively. Simultaneous increases in average fruit size of 2.3 and 2.1% were observed at the first site but not the second. Effects were confined to the season of differential acaricide application and did not carry over into subsequent seasons. Total yield increased with increasing fertilization level in the third and fourth year, as in the first 2 yr. Average fruit size decreased with increasing fertilization level in the third year but not the fourth. Fungicide-nematicide treatments increased total yield and fruit size in both the 3rd and 4th yr. Growth regulator treatments did not significantly affect total yield either year and caused a slight (1.0%) reduction in fruit size in the fourth year. Differential irrigation did not have a consistent, significant effect on total yield, but fruit size consistently increased significantly with increasing irrigation at both sites. Yield reductions from high P. citri populations were greater on nitrogen-stressed trees (16-18%) than on trees that were fertilized conventionally (1-6%) or excessively (0-4%). Total yield and average fruit size did not differ consistently because of any other interactions between effective P. citri treatments and other cultural practices. Marketing conditions continued to favor large fruit; thus, increases in average fruit size on trees where P. citri populations were not effectively suppressed continued to be at least a compensating, if not beneficial, consequence of withholding acaricide applications.