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Disease Management

Crop rotation: Rotations to non-host species or a weed-free fallow are the most effective method of controlling take-all of small grains (Figure 3, extreme left). Because the fungus is a poor saprophyticcompetitor, even a one-year break from production gives almost complete control. During the rotation or fallow period, grassy weeds that can harbor the fungus (Figure 20) should be controlled.


Figure 3	Figure 20

Cultural practices:

Tillage: Although there are conflicting reports from Europe, conventional tillage in the U.S., such as with a moldboard plow (Figure 21), usually reduces take-all over reduced-tillage methods that leave more residue intact on the soil surface. There are three main reasons for less take-all with tillage in the U.S. First, the infested debris is broken into smaller fragments and exposed to more rapid decay, thereby weakening the fungus. Second, burying the crop residue (Figure 22, right) eliminates its soil shading effect and as a result the high soil temperatures of summer kill the fungus. Third, tillage kills grassy weeds and volunteer plants that harbor the fungus.

Weed and volunteer control: The take-all fungus can survive on the roots of grassy weeds and volunteer cereals. When these weeds or volunteer are killed by glyphosate, the defenses of the plant are turned off, because of the mode of action of this herbicide. The take-all fungus can then increase on the dying plant and "green-bridge" to the newly planted crop. Therefore, it is recommended that growers kill out weeds and volunteers at least 2-3 weeks before planting.


Figure 21	Figure 22

Soil drainage and compaction: Good soil drainage produces an environment less conducive to take-all root rot. Therefore, selection of well-drained sites and soil drainage methods should be practiced where possible. Aerification (removal of soil cores) is also effective in reducing disease severity in bentgrass turf areas.

Soil pH: Soil pH can have a profound effect on severity of the disease. Soils below pH=6.0 limit the disease. On the other hand, liming to raise soil pH frequently results in severe take-all. Therefore, crop rotation or a fallow period should be coupled with lime applications.

Seed bed: A firm seed bed for small grains is preferable to a loose one. A firm seed bed reduces the spread of the pathogen along the roots.

Planting date: Delayed planting in the fall reduces take-all by prolonging the time that the fungus is in the saprophytic phase. Because the pathogen is a poor saprophyte, lengthening the saprophytic period weakens the fungus thus exposing it to further microbial activity.

Fertilizers: As a general rule, ammoniacal (e.g. ammonium sulfate) forms of nitrogen reduce the disease over nitrate forms by reducing root surface pH. Some organic soil amendments also have been shown to reduce take-all. Recently, foliar applications of manganese sulfate have been shown to reduce take-all severity on bentgrass turf.

Irrigation: For small grain crops in areas where irrigation is available (Figure 23), applications of water should be as infrequent and deep as possible. Allowing the soil to dry out between irrigations is important to slow down the rate of root colonization and subsequent colonization of the crown.


Figure 23	Figure 24

Maintaining biological control: A natural suppressiveness to take-all can build up in the soil in a monoculture. Fields that show "take-all decline," or those in long-term continuous production of hosts, can show suppressiveness. Unfortunately, rotation to non-grass crops usually eliminates the suppressiveness of a soil and any decision concerning rotations should take this into account. Biological control research using seed treatments with suppressive bacteria (Figure 24, left) on small grains or applying biological agents to established bentgrass has shown promise. Commercial applications of this technology may be available in the future.

Resistant cultivars: Although there are small grain and bentgrass cultivars that have a slight level of resistance to take-all, no highly-resistant cultivars are available. Some level of resistance has been identified in wild grass species that may be transferable into cultivated species. One mechanism for increased resistance is the formation of a barrier or "apposition" by the host (Figure 25) in an attempt to stop penetration by the take-all fungus.


Figure 25	Figure 26

Fungicides: Foliar fungicides have no effect on this root disease of small grains. Two new seed treatment fungicides, silthiofam and fluquinconazole, are commercially available in Europe and the UK, and can reduce and control take-all in certain situations (Figure 26, right) However, these are not registered in the US.

Applications of certain sterol-inhibiting (DMI) and strobilurin fungicides are effective in suppressing take-all symptoms on bentgrass turf and are usually part of an overall management strategy. One or two fungicide applications are usually made in the fall for several consecutive years.

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