May 25, 2007

YELLOWING CROPS

Yellowing fields of barley, wheat and corn are common sites across the region. The yellowing could be from a number of factors:

1. Heat canker: Is caused when hot temperatures occur as the crop emerges. The emerging spike (coleoptile) will have a yellow appearance where the stem contacts the soil line. Often the first leaf will be yellow and is pinched off.
    
2. Cold, cloudy weather and frost:  Yellow small grain and corn fields are most likely the result of cool, cloudy, wet, windy and some instances hail or frost that has occurred this last week. The yellowing is a sign of stress and recent damp, cool weather is the major cause of the yellowing.
    
3. Browning of leaf tips: Some small grain fields also have a brown cast. There are small grain plants having leaves and leaf tips that have turned a tan or white streaked appearance. This is bacteria blight. Bacteria blight will often infect a leaf from a wound or tear in the leaf and spread towards the leaf tip. The infected area will turn a streaked tan or white appearance. This disease is more prevalent on the lower leaves near the soil surface, especially leaves that have been damaged by windy weather. The disease needs damp weather and a wound in the leaf to cause an infection. This disease in not a threat to the crop and fungicides will not control bacteria blight.

SEQ CHAPTER \h \r 1ROLLING PULSE CROPS AFTER  SEQ CHAPTER \h \r 1EMERGENCE

Rolling pulse crops is a common practice to push rocks to the soil surface so they will not interfere at harvest. Rolling allows for higher speeds when swathing or direct combining, and reduces guard and sickle section breakage. The optimum stage to roll pulse crops after emergence is when they 1 to 2 inches high. They can be rolled up to the fifth node stage (about 4 - 6 inches high) without significant yield loss. The growing point remains  below the soil surface until the fifth node stage and rolling up to this stage should not damage the plant. However, rolling past this stage can damage plants, increase the spread of foliar diseases, and reduce yield. The best results of land rolling are obtained when the plants and soil surface are dry. DO NOT roll when the fields are muddy or if the soil is sticking to the roller. Rolling should not be done if the foliage is wet or in the morning when the crop is covered by dew. The best time to roll is during the afternoon, during the warmest part of the day.

SUNFLOWER BEETLE EMERGING

Although populations of sunflower beetle have been low the past few years. It is always a good idea to check fields by scouting for adult sunflower beetles. Adults are ¼ to ½ inch long and look like a Colorado potato beetle except for a reddish-brown head and patch on thorax and exclamation point on the side of the wing cover (see photo). Adults overwinter in the upper 2 to 4 inches of soil and begin emerging from the previous sunflower fields in late May to early June. Beetles overwinter throughout the field and exhibit no preference for field edges or shelterbelts. Early planted sunflower fields will

attract newly emerged adult sunflower beetles first and have higher populations than later planted sunflower fields (late May to June). In the seedling stage, one-two adults per seedling is the recommended economic threshold. A foliar broadcast insecticide spray  will control the emerged adult sunflower beetles. Most sunflower insecticides can be tank mixed with sunflower herbicides. Check label for specifics. If Cruiser Seed Treatment was used, it will also control adult sunflower beetles early in the season.

TAN SPOT FAVORED BY RECENT RAINS

Recent rains will favor continued development of the fungus that causes tan spot infection in wheat. The causal fungus, Pyreonphora tritici-repentis, survives in wheat residue, and when conditions are wet and rainy, the fungus’s fruiting bodies on the straw swell and release spores that can infect the leaves. The early infections appear as small tan to brown spots with yellow halos (see figure of symptoms). NDSU Area Extension specialists are reporting observation of this disease across the state in some winter wheat and spring wheat fields where wheat residue is present. When tan spot is present and wheat crops are in the appropriate stage for early herbicide application, generally the 4-5 leaf stage, a fungicide often is applied or tank mixed with the herbicide application.

Some combinations of products may cause slight injury, so herbicide and fungicide labels should be checked before tank mixing. A spreader/sticker addition is NOT needed for the fungicide, if applied in combination with a herbicide. Early season fungicide use rates generally cost approximately $3.00 to $5.00/acre. A number of fungicides are available for control of early season leaf spot diseases in wheat. These products generally are also registered for barley, if early net blotch or spot blotch should occur. The following table indicates products available and early season use rate.