Weeds, pests and diseases
Garlic has a long growing period and does not compete well with weeds which can seriously affect yields. Ideally, garlic should be planted in areas with low weed burdens which means that weeds should be well managed in the area prior to planting garlic.
The herbicide chlorthal-dimethyl (available under a range of trade names) is the only residual weedicide currently registered for use on garlic.
This post-planting herbicide controls many broad-leaved and grass weeds before they emerge but does not control some troublesome weeds such as fumitory, potato weed (Galinsoga parviflora), wild radish (Raphanus raphanistrum), clover and nutgrass. For current registrations and minor use permits go to the Australian Pesticides and Veterinary Medicines Authority website (apvma.gov.au). Young garlic may also be cultivated by machine between the rows.
Garlic attracts fewer pests and diseases than most vegetable crops.
The major pest is thrips, which are found beneath the leaves and between the leaf base and stem. Thrips are 0.5‑2mm long, mobile and feed by rasping. Small white patches appear on the leaves and the bulbs may shrivel. Other pests include red-legged earth mite, aphids, snails and nematodes. The most common disease is downy mildew (affecting the leaves). For current pesticide registrations and minor use permits go to the Australian Pesticides and Veterinary Medicines Authority website (apvma.gov.au).
Plants may also be damaged by several diseases on the leaves and bulbs in the field and the bulbs in storage particularly with high relative humidity. Check with the AVPMA for current registered chemical control measures and those chemicals covered by minor use permits.
Yields and quality of garlic plants are reduced by virus infections. It is believed that most garlic in Australia is affected by three types of viruses which may appear as a yellow streaking of the whole plant, or have no visual symptoms. In future, it may be possible to obtain virus-free planting material in Australia.