Be prepared this spring, pests are starting to emerge in fields and tunnels.
Wireworm:
Has been detected in tunnels already, predating mainly early leafy greens. As the soils warm they will be coming close to the soil surface in search of roots and stems to eat. If you see individual plants yellowing and wilting, pull them up with the roots and you’re likely to see a wireworm in the root ball as the below pictures show. As the roots and vascular system of the plant are eaten, you will see wilting and yellowing as the leaves can’t get moisture or nutrients.
Leek moth:
This pest predates all alliums (onions, garlic, leeks, etc) not just leeks as you may suspect from the name. Garlic is most heavily damaged by this pest as often onions and leeks are not in the field when the first flight occurs.
The first flight is expected to occur in the next couple of weeks. We, in NS, do not have the modelling data yet to accurately predict this flight but a good rule of thumb is when the average temperature reaches 10 °C for two days in a row. This first flight is from over-wintering moths. It is crucial to protect your alliums with insect netting or row cover as a heavy pest pressure from the first flight will dramatically increase the larval presence and damage later in the year when all of your alliums are in the field.
They are nocturnal so you may not notice them until their larvae are creating window-pane like damage to your onions, leeks, and garlic. They are difficult to control once they establish themselves, as they live inside of the leaves of onions or will bore their way into the stems of garlic and leeks, making the plants unmarketable. They generally have two flights here, one early in the spring and another later in the summer before garlic harvest. A warm summer may allow for a third flight depending where in the province you are.
Physical barriers such as row cover and insect netting will help to prevent the laying of eggs on your alliums.
Onion, cabbage, and seed corn maggot:
These each overwinter in the soil then emerge in the spring, generally towards the end of May. The cabbage maggot flies emerge first, followed by onion maggot flies, then seed corn maggot flies. Generally you’ll first notice the presence of these maggots when transplants start wilting on hot days. This is due to the larvae feeding on roots; plants will eventually die if left unchecked. On a small scale, physical barriers (such as row cover, insect netting, etc) are effective. On a larger scale chemical controls are available to help manage these pests.
Cold wet spring:
While not a pest, you may be seeing signs of the relatively cold and wet weather on your plants leaves right now. Cold wet weather slows soil microbial metabolism, meaning that overwintering plants like garlic might be showing yellow leaf tips right now. This is most likely due to cold soils slowing the mineralization of nutrients, and is mainly a challenge in organic systems where amendments require microbial mineralization to be plant available. This can be remedied by applying a plant available nitrogen source such as a liquid fertilizer or urea. In addition to reduced mineralization rates, the cold wet weather was an excellent environment for promoting fungi such as Pythium, Rhizoctonia, and Smut.
Reach out to me to discuss any of these pests, or if your crops are suffering for other reasons.
Happy seeding and transplanting!
Tim (tmorcom@perennia.ca)
