Corn and Soybean Disease Concerns

Transcription

1 Atlantic Corn, Soybean, Cereal & Oilseed Growers Symposium February 12 th, 2014 Corn and Soybean Disease Concerns Bill Thomas

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4 Corn: Anthracnose Northern Corn Leaf Blight Eye spot Yield reductions, reduced bushel weights

5 Soybean: Brown Spot Bacteria blight White mold

6 Anthracnose Leaf Blight and Stalk Rot of Corn Colletotrichum graminicola Symptoms first seen and confirmed in Nova Scotia in Number of fields with confirmed disease increased from 4 in 2012 to 16 last year last year. Leaf blight phase and stalk rot phase. Leaf blight can cause premature plant death that interrupts filling of the grain; losses could be as high as 10 to 15%. Stalk rot can cause severe stalk lodging that leads to high yield loss. Anthracnose can attack a corn plant at any stage of development.

7 Anthracnose Lesions can be seen on leaves soon after plant emergence when the fungus has overwintered in the field.

8 Anthracnose The size and shape of the lesions varies with hybrids making diagnosis in the field difficult. Using a hand lens the presence of small black spines (Setae) arising from the surface of the leaf will confirm the disease. Lesions are generally brown oval to spindle shaped ; usually a yellow orange area surrounds the disease portion of the leaf.

9 Anthracnose Leaf blight that has been observed on the lower leaves of young plants in early June will often not show any further disease spread until after tasseling.

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12 Anthracnose is favoured by warm wet weather. Long periods of overcast weather with high humidity and free moisture on the leaves can result in severe leaf infection. Yield reductions can be expected when significant leaf death occurs before six weeks after tasseling.

13 Anthracnose Control Hybrid selection is the first step. Hybrids very widely in their level of susceptibility to anthracnose. Hybrids resistant to leaf blight might not be resistant to stalk rot. Since anthracnose survives in corn residues, especially on the soil surface the disease may be more serious under reduced tillage systems and continuous corn. Tillage systems that chops and completely buries the residue coupled with a oneyear rotation away from corn will reduce the local source of inoculum. A two year rotation away from corn for no-till or reduced till systems is recommended. Reduce plant stress by using a balanced soil fertility program, proper plant populations and good insect & weed control.

14 Northern Corn Leaf Blight Setosphaeria turcica First confirmed in the province in 2004? NCLB prevalence has increased since 2010 NCLB can cause yield loss if the disease develops before or during the tasseling and silking phase. Hybrid susceptibility, cropping practices and weather strongly influence disease development.

15 Northern Corn Leaf Blight Early symptoms appear as long narrow lesions that run parallel to the leaf margins.

16 Northern Corn Leaf Blight The early lesions develop into the classic cigar shaped tan lesions.

17 Northern Corn Leaf Blight Lesions generally range from 1 to 7 inches long.

18 Northern Corn Leaf Blight Under high humidity olive green or black fungal spores will appear in the lesions

19 Northern Corn Leaf Blight NCLB fungus survives through the winter on infected corn residue. As temperatures rise in the spring and early summer the fungus spores which are rain splashed or wind blown onto leaves of the new corn crop. Infection occur during periods of warm, wet and humid weather. Lesions typically appear 7 to 12 days after infection. The more lesions and the earlier they occur the greater the loss of photosynthetic area and the larger the potential yield loss.

20 Northern Corn Leaf Blight If lesions reach the ear leaf or higher and become so numerous as to destroy the leaves before or just after tasseling yield loss can be as high as 30% - 50%. If leaf damage is moderate or delayed until 6 weeks after silking yield losses are minimal. There is not a clear relationship between the amount of leaf tissue covered by lesions and yield loss. Weather is the primary factor causing disease, but notill or reduced tilled fields planted to susceptible hybrids are at highest risk. Fungicides are available to help manage the disease.

21 Northern Corn Leaf Blight Symptoms vary by hybrid susceptibility. There are several races of the fungus. Hybrids with partial resistance to NCLB typically produce fewer and smaller lesions with fewer spores.

22 NCLB Control Select hybrids with moderate resistance. This will delay the progress of the disease to protect against yield loss. Seed companies indicate hybrid resistance with a numerical rating. Continuous corn, no-till and reduce tillage systems are at high risk for disease development. For infected fields one year rotation out of corn followed by tillage. For no-till or reduced tilled fields a two year rotation out of corn maybe needed.

23 Eye Spot Aureobasidium zeae The disease is commonly associated with continuous corn and reduced tillage practices. The adoption of high-residue farming practices has contributed to the increasing importance of eyespot in the area.

24 Eye Spot The fungus survives in corn residue and spores are produced on the residue under moist conditions. These spores are splashed or blown by wind onto corn leaves. Leaf wetness is required for infection, so rainy conditions or persistent dews will result in disease outbreaks.

25 Eye Spot If the disease spreads to the upper leaves it can cause considerable destruction of photosynthetic leaf area, resulting in yield reduction. Severe disease will predispose the corn plants to stalk rots.

26 Eye Spot Control Some hybrids are less susceptible to eyespot and may be recommended by your seed supplier. If the disease was severe in your area last year or if eye spot was in the field last year grow resistant hybrids. Rotation with crops other than corn allows the corn residue to decompose and the fungus will die before another corn crop is planted. Usually one year out of corn will reduce the inoculum adequately to grow another corn crop, but it may take longer under reduced tillage conditions. There are effective fungicide sprays available but they are seldom recommended.

27 2013 Fungicide Efficacy Trial - Cornell University Cornell University Cooperative Extension Managing Corn Diseases

28 Soybean Brown Spot Septoria glycines Becoming more common. Found on soybean residue and spreads from the soil to young soybean plants by splashing rain. Infection occurs as early as V2 growth stage causing small irregularly shaped brown spots or lesions on the lower leaves.

29 Soybean Brown Spot Brown spot does not usually affect soybean productivity unless more than 25-50% of the canopy defoliates prematurely. Severe Brown Spot leading to large leaf loss at the R2 to R3 stage can reduce yields by as much as 15%. -Frequent rainfall is the primary condition for severe Brown Spot

30 Bacterial Blight Pseudomonas syringae Comparison of brown spot right and bacterial blight right

31 Soybean Brown Spot and Bacterial Blight Management of the two diseases is similar: Use disease tolerant varieties. No resistant varieties are available but field tolerance has been observed. Use disease free seed Control Rotate soybeans with corn or forage Bury residue. Clean tillage reduces the risk of the disease significantly.

32 White Mold Sclerotinia Stem Rot Sclerontinia sclerotiorum In severe cases the disease can cause more than 50% yield reduction When white mould or Sclerotinia is found in our soybean crops it is usually because the rotation has had a history of too frequent cropping soybeans, canola, carrots, potatoes or other susceptible hosts.

33 White Mold Overwinters in the soil in a special structure called a sclerotia. Sclerotia can survive in the soil for about seven years in the absence of a host plant.

34 White Mold Infection occurs during flowering. If after the canopy develops there are low soil temperatures (less than 15 0 C ) and high soil moisture the scelrotia on the soil surface and within 2 of the soil surface will germinate and produce apothecia. The apothecia produce wind blown spores that infect the soybean plants.

35 White Mold As infected plants begin to wilt, upper leaves turn grayish green than brown. Dead soybean plants are usually seen clustered in infected fields in late August or early September Most typical sign of the disease is the masses of white cottony, fungal mycelium growing on the lesions of infected stem.

36 White Mold -Control An integrated management plan is needed to control White Mold in soybeans; Avoid a row spacing of less than 15 inches in fields where white mold has been a problem in the past. Deep tillage to bury sclerotia can reduce germination of the apothecia. Rotate out to a non-host crop (corn & forage grasses). Avoid planting soybeans after susceptible crops such as sunflower, carrots, canola, potatoes and edible beans. Practice good weed control lambsquarter, redroot pigweed, mustards are all hosts.

37 Rotation Rotation Rotation

38 Rotation Sequence Grain Corn Yield (t/ha) Grain Corn Yield (t/ha) Loam Soil ( ) Clay Loam ( ) Continuous Corn Soybean-Corn Soybean-Winter Wheat-Corn Soybean-Wheat (RC)-Corn Soybean-Wheat (RC)-RC*-Corn RC* is red clover that was not fall plowed, but allowed to grow into September of the 2 nd year Source: Dr. T Vyn at U. of Guelph

39 Dairy (forage based) crop rotation considerations In a perfect world : A 7 year rotation with 3 production years alfalfa/grass mix, then grain corn, soybeans, silage corn & back to direct seed forages Or a 8 year rotation, with 4 forage years (3+1) and corn-soybean-winter wheatcorn

40 Dairy (forage based) crop rotation considerations Rotation problems occur when farms don t have enough well drained, alfalfa-corn type land (these farms often tend to grow corn for 2-4 years in a row). This ignores the basic rule of crop rotation, that a crop should never follow itself.

41 Final Comments Genetic Resistance - select high-yielding hybrids and cultivars with the appropriate level of disease resistance and other key traits needed for your field. Scout your fields regularly management starts with awareness Tillage - encourages breakdown of crop residue, reducing disease inoculum. Reduce plant stress field selection, use a balanced soil fertility program, proper plant populations, good insect & weed control. Crop rotation is critical - at least 1 year out of corn; 2 years for no-till or min-till systems.

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