Posts Tagged ‘garlic’

Garlic Bloat Nematode Found in Several Garlic Samples

Friday, May 11th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu and Karen Rane, Extension Specialist Entomology, University of Maryland rane@umd.edu

This must be a bad year for garlic because besides finding bulb mites we also have found garlic bloat nematode in several samples of damaged garlic. I wrote about this nematode last year and advised garlic growers to watch for it and to test any bad looking bulbs for it. This year growers are sending in their bad looking garlic bulbs and unfortunately many are infested with this nematode. The garlic bloat nematode Ditylenchus dipsaci can destroy a crop of garlic in one season. It probably came from Canada in garlic that was imported for food, but was planted as seed garlic. The problem then spread through distributors because there is no certification program for seed garlic and is it now widespread throughout New York. Symptoms of bloat nematode in garlic plants include: bloated, twisted, swollen leaves, distorted and cracked bulbs with dark rings (Fig.1).

Infested tissues become spongy, distorted and predisposes the plant to other problems like fusarium or white rot (Fig. 2) and bulb mites. These nematodes also can move to the inflorescence and remain in seeds for long periods of time in some plant species, i.e., beans, clover, and alfalfa where they are major sources of nematode dispersal. The nematodes can be spread around fields by equipment or on clothing and shoes. Garlic bloat nematodes can overwinter in soil or crop debris. If a grower has purchased or brought in new planting material over the last few years, especially if it came from Ontario or New York, you may have this pest. If you have not made any new introductions in a while you are probably safe. If you have garlic bulbs that look something like they do in figure 1 or 2 you should send a sample to a nematode laboratory for testing.

 

Fig. 1 The lack of roots on one side of plate and bulb deformation can be indicators of bloat nematode infection.

To prevent build-up of the nematode populations in a field, rotate away from any Allium crops (garlic, onions, and leeks) and control nightshades for at least 4 years. Another method to reduce levels of bloat nematodes in the soil is to keep the fields where garlic was grown moist, because bloat nematodes cannot survive for long periods in moist soils. They can persist for several years though, in dry soil and on dry plant residue. Bloat nematodes can actually survive better in dried crop debris than in soil.

Growers can use soil fumigants to reduce or eliminate the nematodes from infested areas of the field. Growers can also use bio-fumigant cover crops that can be planted after harvesting garlic. Mustard, sorghum-sudangrass 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.

Fig. 2 Non-infested garlic bulbs (left) and infested garlic bulbs (right) with bloat nematode

Bulb Mite Found in Problem Garlic Fields

Friday, May 11th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu and Karen Rane, Extension Specialist Entomology, University of Maryland rane@umd.edu

Several garlic fields have been having problems the last few years with rotting bulbs. Some seedcorn maggot was found feeding on the bulbs and we thought this was the major problem. But damage continued beyond what the maggots could do. On a second look very tiny bulb mites were found in the damaged garlic. Bulb mites are a problem of garlic and sometimes of onion that usually goes unrecognized (as in this case). These pests can reduce stands, slow plant vigor, and increase post-harvest diseases by their feeding on the roots and the stem plate. Bulb mites have a very wide host range, but cause most of their damage to onions and garlic. These mite pests are usually not seen on the bulb and prefer crawling into crevices between the roots and stem plate.

The best way to determine whether these mites are present is to carefully dissect the region where the roots and bulb come together. The mites also could be under one or two layers of scales at the lower end of the bulb. There are usually other mites present, but with a hand lens the bulb mites usually can be identified from other mites.

The mite is bulb shaped with its legs moved forward and a bulbous rear end and many long fine hairs (Fig. 1). The mouthparts and legs are purplish-brown while the main body is creamy white. These mites have been described as looking like tiny pearls with legs. The mites are extremely small (from 0.02 to 0.04 inches) and are very slow moving. They are usually found in clusters underneath scales and at the base of the roots.

It is not just the direct feeding of these mites on garlic and onions that causes problems, but also their feeding allows pathogens to enter through the wounds they create. These wounds are very good entry points for pathogens like Fusarium spp., Sclerotium cepivorum (causes the disease white rot), and various soft-rotting bacteria. The white rot fungus does best in cool temperatures, and symptoms include white fungal growth on the stem or bulb with small, dark structures called sclerotia in the decayed tissue (Fig. 2). Early in the growing season, bulb mites can cause poor plant stands and stunted growth as they feed on the plants (Fig. 3). Infested plants easily can be pulled out of the soil because of the poor root growth. Later in the season, higher than normal amounts of soft rot and Fusarium dry rot may be seen because of the wounds caused by these mites (as we saw in a couple of the garlic fields).

Figure 1. Garlic bulb mites greatly magnified

Bulb mites survive in the soil on organic matter left behind from the previous crop. As long as there is decaying allium vegetable matter in the soil, bulb mites can survive in the field. The best way to control bulb mites is to allow the vegetation from the previous crop to breakdown before any new crop, especially garlic or onions are planted again. Low areas of the field that stay wet and have high levels of organic matter are especially prone to greater bulb mite survival. 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. Effective hot water treatment will also, unfortunately, reduce bulb vigor.

 Figure 2. White rot (white fungus) with microsclerotia (arrows) in garlic stem

 Figure 3. Garlic plants damaged by bulb mite feeding and invasive fungi

Nematode Pest Recently Found in New York Garlic Fields May Also Affect Mid-Atlantic Growers

Thursday, May 12th, 2011

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

There is a new ‘old’ pest infecting garlic and onions in New York and other New England states that has been found as far south as Pennsylvania. It is the garlic bloat nematode. The garlic bloat nematode Ditylenchus dipsaci is capable of severely damaging a field of garlic very quickly. It probably came from Canada in garlic that was imported for food, but was planted as seed garlic. The problem then spread through distributors because there is no certification program for seed garlic and it is now widespread throughout New York. Symptoms of bloat nematode in garlic plants include: bloated, twisted, swollen leaves, distorted and cracked bulbs with dark rings (fig.1). Infested tissues become spongy, distorted and predisposes the plant to other problems like fusarium or white rot (fig. 2). Garlic bloat nematodes can overwinter in soil or crop debris and can move to the inflorescence and remain in seeds for long periods of time in some plant species, i.e., beans, clover, and alfalfa, which act as major sources of nematode dispersal. The nematodes can be spread around fields by equipment or on clothing and shoes. If a grower has purchased or brought in new planting material over the last few years, especially if it came from Ontario or New York, you may have this pest. If you have not made any new introductions in a while you are probably safe. If you have garlic bulbs that look something like figure 1 or 2 you should send a sample to a nematode laboratory for testing.

To prevent build-up of the nematode populations in a field, rotate away from any Allium crops (garlic, onions, and leeks) and control nightshades for at least 4 years. Another method to reduce levels of bloat nematodes in the soil is to keep the fields where garlic was grown moist, because bloat nematodes cannot survive for long periods in moist soils. They can persist for several years though, in dry soil and on dry plant residue. Bloat nematodes can actually survive better in dried crop debris than in soil.

Growers can use soil fumigants to reduce or eliminate the nematodes from infested areas of the field. Growers can also use bio-fumigant cover crops that can be planted after harvesting garlic. Mustard, sorghum-sudangrass 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.

Figure 1. The lack of roots on one side of plate and bulb deformation can be indicators of bloat nematode infection.

Figure 2. Non-infested garlic bulbs (left) and infested garlic bulbs (right) with bloat nematode