Controlling Onion Pests and Diseases

It is particularly important to ensure that environmental and growth constraints do not limit bulb formation and bulb quality.

Control of pests and diseases, will minimize rots and storage disorders.

Soil sterilization and good rotational practices are important in helping minimize disease problems. A good crop nutrition is essential to make onion and garlic crops less susceptible to pests and diseases. There are several important pests that attack onions and garlic, like nematodes, stem and bulb eelworm, thirps and onion fly or maggot.

Onions are also very prone to foliar diseases and bulb rots, such as slimy or ‘sour’ outer scales, a bacterial disease that significantly reduces onion bulb quality.

Fungal diseases such as neck rot, mildew, rust and leaf rot, are frequent too. Fungicidal control is required on these cases.

onion sour scales

Neck rot

Crop Nutrition and Onion Pests and Diseases

Optimum nutrient management during establishment and vegetative growth are needed to ensure nutrients don’t limit bulb quality.


Nitrogen is required to maximize bulb dry matter and size. However, too much nitrogen softens the bulb and increases storage rot diseases. Excess N can also thicken the neck, resulting in greater disease entry. In addition, crops with phosphorus and manganese deficiencies tend to have thicker necks at maturity. Later applications of nitrogen result in greater thickness as well. It is critical to get the balance and timing of nitrogen right to maximize yield without adversely affecting storage quality.


Calcium is particularly important for bulb density, integrity and long-term storage with minimal disease problems. Calcium has a major role to play in promoting long-term storage quality with minimal diseases problems. Trials confirm that onion crops with high levels of calcium in the bulbs have reduced levels of black rot due to Aspergillus niger and also less neck rots such as Botrytis allii.