Cover Crops for Managing HLB

By Davie Kadyampakeni and Miurel Brewer

Row middle management is a key area that can improve tree performance. Row middles encompass 80% of citrus orchards, and 70% of the root system of citrus trees was located in row middles before huanglongbing (HLB). Typically, Florida citrus growers manage row middles using physical, chemical and mowing practices, often leaving them free of vegetation. However, environmental pollution concerns due to the heavy use of synthetic fertilizers and herbicides have increased interest in alternative management practices such as cover cropping.

Before the 1950s, cover crops were widely planted, but this practice declined with the accessibility of fertilizers and pesticides. Nevertheless, cover cropping has seen a resurgence due to its benefits of increased yields, improved water-use efficiency, nutrient cycling and reduced nutrient leaching.

Effective cover crops should be low-cost, produce high dry matter, establish easily, germinate quickly and be drought-tolerant. They can modify soil properties, including chemical, physical and biological characteristics. Mixtures of cover crops can maximize benefits compared to monocultures. For example, legume and grass mixtures can fix nitrogen (N) and sequester nutrients, respectively.

In perennial systems like citrus orchards, cover crops can play a crucial role in improving soil quality and mitigating pest and disease pressures. Brassicas, such as mustard and daikon radish, are known for their biofumigation properties, which can suppress soil-borne pathogens and pests. Grasses, such as sorghum, rye and oats, are effective at preventing soil erosion, improving soil structure and scavenging nutrients from deeper soil layers.

Combining brassicas, grasses and legumes in cover cropping systems can provide complementary benefits. Brassicas can suppress pests and diseases. Grasses can improve soil structure and nutrient uptake. Legumes can fix atmospheric nitrogen, enriching soil fertility.

Cover crop residue management significantly impacts soil mineralization rates for carbon (C) and N. Incorporating residues into the soil accelerates decomposition by improving contact with soil microorganisms. Leaving residues on the soil surface creates a mulch layer beneficial in high-temperature subtropical climates like Florida. The composition of cover crop residues, including starch, sugar, protein, cellulose and lignin content, influences decomposition rates.

University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) work for the past four to six years has shown that growing cover crops has potential to increase soil organic matter, improve soil nutrient/water holding capacity and sustain grove productivity over time. Cover crops evaluated in mostly Central and Southwest Florida include cowpea, sorghum-sudangrass, oat rye, daikon radish and sunn hemp.

Davie Kadyampakeni is an associate professor, and Miurel Brewer is a research associate, both at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

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