Use More Micronutrients for HLB

HLB-affected citrus trees benefit from micronutrients at higher-than-recommended rates, Tripti Vashisth reported in a virtual Florida Citrus Growers’ Institute presentation. Vashisth, a University of Florida Institute of Food and Agricultural Sciences researcher, said that a 20 percent higher-than-recommended rate of micronutrients can improve productivity in trees with HLB.

The Florida Citrus Growers’ Institute is normally held in Avon Park in April and attended by hundreds of growers. The in-person event was cancelled this year due to COVID-19, but many of the scheduled presentations are now available online.

Take-home messages from Vashisth’s presentation included these points:

• A constant supply of nutrients and soil acidification is beneficial.

• The fertilizer program should be site specific to address specific tree needs.

• Soil-applied micronutrients are better than foliar micronutrients.

• The preferred soil pH range for current Florida citrus is 5.8 to 6.5.

• Due to the HLB-affected tree’s small root system, the fertilizer supply should be constant to the tree. Use small and frequent doses.

• Focus on leaf nutrient analysis rather than the rate of fertilizer applied; trees perform better when they are in the high end of the optimum range.

The recommendations Vashisth offered were based on research findings she reported throughout her presentation. Following are some of those findings:

• Roots of HLB-affected trees are functional in nutrient uptake. They have a high requirement for certain secondary nutrients and micronutrients.

• HLB-affected trees and roots are highly efficient in nutrient uptake.

• Added stress of nutrient uptake to meet shoot requirement may result in rapid decline of roots.

• Good fertilization improves plant defense response.

• HLB symptoms intensify under high soil pH.

• Root density is related to bicarbonate stress, thus reducing yield at high pH.

• Healthy trees are not affected by soil pH as much as HLB-affected trees are.

• Performance of HLB-affected trees and healthy trees are comparable at low pH.

• At low pH, HLB-affected trees have enhanced plant defense.

See Vashisth’s full presentation here.