Growing garlic is an incredibly rewarding experience, but it can also be frustrating. Garlic is a high value horticultural crop in the onion family. Farmers are getting interested in growing garlic due to its reported high returns and the readily available local market. But wait, have you considered that like any other crop, garlic growing can result in massive losses?
Well, some new growers think garlic is ‘bullet-proof’ and that it can repel insects and that nothing can attack it. But the truth is some farmers have reported cases of garlic destruction from pests and diseases.
Garlic is effective against a wide range of disease-causing organisms and insects at different stages in their life cycle but, there are several primary problems that can beset garlic; soil nutrient imbalances, irrigation variance, seasonal weather variation, insect pests, fungi and viruses. Most of these are manageable.
Prevention is usually the easiest way to deal with growing problems. By maintaining a good organic garden soil, most of these problems can be eliminated or lessened.
When you don’t get the growing results you had hoped for, how do you find out what you have and how it happened? That is what I will tackle today. Bulb mites are extremely tiny and a problem of garlic and sometimes of onion that usually goes unrecognised — until too late.
These pests can reduce stands, slow plant vigour, and increase post-harvest diseases by their feeding on the bulb, roots and the stem plate. Bulb mites have a wide host range, but cause most of their damage to onions and garlic. These mite pests prefer crawling into the crevices between the roots and stem plate where they feed. It is not just the direct feeding of these mites on garlic that causes problems, but also that their feeding allows pathogens to enter through the wounds they create.
Early in the growing season, bulb mites can cause poor plant stands and stunted growth as they feed on the plants. Infested plants can be pulled out of the soil because of the poor root growth. Later in the season, higher than normal amounts of soft rot may be seen because of the wounds caused by these mites.
The best way to control bulb mites is to allow the vegetation from the previous crop break down before any new crop, especially garlic or onions are planted again. These mites may also come into a clean field on infested garlic cloves. The use of clean garlic clove seed or seed that has been hot water treated will control these pests.
Stem and bulb nematode can destroy a crop of garlic in one season. Invasion of the stem tissue occurs first, causing stunting, twisted, and pale leaves, usually followed by rotting of the lower stem and base of the bulb. In severely infested fields, young plants become enlarged and deformed and frequently die. The nematodes are primarily located in infected tissue, so to control this pest, infected plants should be removed by digging and then burned.
Other control measures include planting clean seed stock, elimination of volunteer garlic and onions, and proper rotation. Do not plant garlic following any member of the onion family, or alternate hosts such as pea, parsley and celery.
To prevent build-up of the nematode or mite populations in a field, you must rotate away from any Allium crops (garlic, onions, and leeks) and control nightshades for at least four years. Do not keep any bulbs or seed from an affected field no matter how clean it looks. You should start from fresh seed or bulbs.
Rotation to areas of the farm that have not had garlic or onion plantings for many years with new garlic or onion seed is the best method of control. Use soil fumigants to reduce or eliminate the nematodes from infested areas of the field.
Growers also can use bio-fumigant cover crops that can be planted after harvesting garlic. Mustard and sorghum-Sudan grass have been shown to reduce nematode populations due to the bio-fumigant constituents they produce. Be sure to clean equipment and storage areas with meticulous sanitation techniques. Garlic is a weak competitor against vigorous weeds. Weed management is essential and can be undertaken by cultivation, hand hoeing, mulching or with herbicide applications. Avoid deep cultivation close to the plants, as root damage and subsequent yield losses may occur. If weeds are not controlled early, they can easily overtake young garlic plants, causing significant yield losses.
HARVESTING AND CURING
Knowing when to harvest has always been tricky. Different varieties will often mature at different times. Harvesting too early will result in small bulbs that do not store well. Harvesting too late will force the cloves to pop out of the skins, making them susceptible to disease and resulting in unmarketable bulbs. To harvest, the bulbs should be dug with the shoots and roots still attached.
After digging the plants, they should be tied in bundles of 10 to 15 and allowed to dry in a well-ventilated room. After about three to four weeks of curing, the shoots and roots should have dried down. The tops should then be cut about one-half to one inch above the main bulb and roots should be trimmed close to the base of the bulb. Clean bulbs by removing the outermost skins, being careful not to expose any cloves. Any remaining soil should be brushed away. Bulbs are then graded for market.
Optimum storage conditions will depend on whether the garlic is to be used for table stock or planting stock. Table stock garlic is best stored at 32 degrees to 40 degrees fahrenheit and a relative humidity of 60 to 70 per cent. Table stock garlic can also be stored at room temperature and 60 to 70 per cent relative humidity, but will dehydrate faster than if stored at 32 degrees to 40 degrees fahrenheit. Temperatures between 42 degrees and 52 degrees fahrenheit will cause sprouting, and humidity greater than 70 per cent tends to promote rooting.
Planting stock garlic should be stored at room temperature and 60 to 70 per cent relative humidity. Garlic stored at 32 degrees to 40 degrees fahrenheit and then used for planting will not bulb properly. The bottom line is that each grower of garlic has to learn to identify the cause of problems in their garlic and find out for themselves what to do about them.
In summary, before you get into garlic farming, make sure you do thorough research.
The writer is a consultant/advisor on sustainable agricultural innovations. (By George Mbakahya)