ISSUE 8 June 25, 1998
REPLANTING DECISION IS FUNCTION OF DATE AND STAND
The decision of whether to replant a row crop with a reduced stand is a function of the calendar date plus the stand that is available. Excessive rain, hail and cutworm activity have all taken their toll in reduction of row crop stands.
Reduction in stand is the major factor in deciding to replant row crops. As we move later in the season, the decision of how much stand to keep changes, because if we tear up the field and reseed, the late plantings have much less yield potential.
With corn, around June 10, with stands of about 14,000 plants per acre, we probably would want to tear it up and replant to a crop like sunflower, that can be planted at this date and still mature. By June 15, the decision may be to keep a stand of 14,000 to 16,000 plants per acre because it is too late to plant an alternative.
Uniformity of stand is the key to evaluating a poor stand. If there are no large skips in the field, fairly low populations of soybeans, dry beans and even sunflower can still maintain yields. These plants have the ability to branch and fill in space. This is not true with corn and weeds become a bigger problem.
With half a stand of soybeans, dry beans or sunflower, you may want to leave them. If less, you may want to replant to an earlier variety or switch to another crop. About the only choice in the 4th week of June is flax, early-short season sunflower or millet. Also, one must take into consideration the herbicide used in the prior planted crop and will it create a problem with injury to a crop change.
WILD OATS MAKES GOOD HAY
Difficult farming conditions this season will likely interfere with some weed control plans and, coupled with abundant soil moisture, result in areas of severe wild oat infestation. Producers with field areas heavily infested with wild oats might consider these areas as a hay source rather than cultivating them to kill the wild oat plants.
Wild oats makes excellent quality hay. The way to get good quality wild oat hay is to cut early, just as the head is emerging from the boot, when the protein content is highest. Equally important is cuttingand killingwild oats before the seed has a chance to develop.
Never allow the wild oat plant an opportunity to mature and shatter seed. It is possible to have up to 800 seeds produced by a single plant. The number of seeds per plant is much less in thick stands, but 20 bushels per acre of shattered seed is not uncommon.
Failure to control wild oats now will mean paying the price later. Farmers can help themselves by making a good quality hay and controlling wild oats at the same time.
HAIL DAMAGE IN ROW CROPS
Hail damage to crops occurs somewhere in the state every year. Reports have already been made of hail in a number of areas of the state. When hail damage occurs on corn, soybean, dry bean and sunflower early in the growing season, replanting is possible; but deciding whether to replant is usually difficult. Total stand reduction, leaf loss, stem injury, weed control, and calendar date are factors to consider when making this decision.
Corn: The growing point remains below ground 2-3 weeks after the plant emerges (4-leaf). If the growing point is not damaged, corn will recover and perform better than replanted corn. Split the stalk down the center and inspect the growing point. If normal, it will appear white in color and firm in texture. Injured growing points will appear brown or discolored 2-3 days following the hail. Complete loss of leaves early to corn when small usually does not greatly affect grain or silage yields.
Soybean and Dry Bean: The growing points of beans are located in the top of the plant and in leaf axils. Growing points of beans are easily damaged by hail soon after emergence. Regrowth will not occur if hail stones cut the stem off below the cotyledonary node. If the top of the plant is damaged, regrowth can occur from one or more axillary buds. Bean stems may be bruised or broken. The damage may not be severe enough to kill the plant. However, the plant may lodge later as the callus tissue is weak and cannot support the pod weight. Reduction in soybean stands to four plants per linear foot of row can still produce fair yields.
Sunflower: Sunflower may be more tolerant than beans, but the degree of hail tolerance depends on the intensity of the hailstorm and the stage of growth. Sunflower is least tolerant during the seedling and budding stages, and most tolerant after flowering. Hail damage may be direct or indirect. Direct damage results from stand reduction, loss of recoverable heads because of severely bruised or broken stems, and head shatter at later stages. Indirect damage results from defoliation and disease infestation to injured plant tissue.
Research conducted on simulated hail losses in sunflower indicated that a one-to-one relationship does not exist between stand reduction and yield loss. A 50% stand reduction resulted in only a 28% yield reduction. Defoliation of sunflower by hail was reported to be most damaging during the bud stage. Defoliation of 80% at the bud stage resulted in yield reduction of 53%. Whereas 80% defoliation at the 50% mature stage resulted in only a 12% yield loss.
Duane R. Berglund
NDSU Extension Agronomist
APPROACHING CRUCIAL SMALL GRAIN STAGES
Small grain crops around North Dakota are approaching critical development stages. While developmental covers a wide range of stages much of the crop, particularly the early planted portion, is in the boot and early stages of flowering.
Two pests, scab and wheat midge, become problems during heading and flowering. From heading to flowering is when wheat is susceptible to the wheat midge. Once flowering is complete wheat midge no longer attack the developing heads. Wheat midge is not a problem on barley. Flowering is also when wheat is most susceptible to scab infection. Barley flowers in the boot and is most susceptible to scab once heading occurs.
Monitoring heading in barley and wheat is extremely critical for effective control of either pest. The time required for both wheat and barley to go from mid boot to head emergence can range from three to five days. Obviously environmental conditions have a large impact on the developmental rate. Warm sunny days favor rapid development.
Growing degree days (GDD) can be used to predict when heading will occur (See May 7, 1998 Pest Report). Both wheat and barley will require about 140 GDD to go from mid boot to heading. Wheat will require about 270 GDD to go from mid boot to completion of flowering. The NDSU NDAWN system (www.ext.nodak.edu/weather/ndawn/listgdd.html) provides GDD for several regions around the state.
Even though the past several weeks have been quite cool early planted crops are developing rapidly. Development rate of barley at Fargo and Prosper this year has exceeded rates predicted using a GDD model.
The important point is, if you plan on controlling wheat midge or scab with a pesticide application, timing application with development is crucial to success. Knowing the stage of a crop now and when it will head or flower is useful when planning for the pesticide application.
Control of scab with a fungicide depends on correct timing of the application. The optimum time for fungicide application on wheat is at 25% flowering and after heading is complete in barley. Fungicides only provide protection against scab on tissue that receive a direct application. Even though fungicides like Tilt and Folicur are systemic they do not move throughout the plant but remain in a localized area near the site of absorption. Applications before heading is complete in both wheat and barley will compromise control of scab.
MELANISM VS BLACK CHAFF
The recent heavy rainfall favors the development of several diseases in wheat and melanism which can easily be mistaken for disease. Melanism, a genetically controlled discoloration, is often confused with black chaff.
Black chaff is a bacterial disease that affects the glumes of developing wheat heads. Symptoms consist of dark lines or patches on glumes and dark lesions on the awns. The lesions often result in alternating green and brown areas on the awns which aids in identifying the disease. Black strips are also diagnostic of black chaff. Leaf symptoms are dark water soaked longitudinal streaks that result in tan or brown dead tissue.
Melanism, or false black chaff, produces dark purple to black streaks or blotches on the glumes. This dark discoloration is usually more uniform than black chaff. The awns and peduncle show no symptoms. The formation of a dark purple to purple brown ring at each joint is indicative of melanism and can be used to diagnose this disorder. It is often necessary to peel away the leaf sheath to see these rings.
Melanism is not thought to reduce yield in currently grown varieties. Development of melanism usually occurs with hot humid weather; consequently, a period of hot weather following the recent rains could result in substantial amounts of melanism.
NDSU Extension Agronomist, Small Grains
MUSHROOMS AND FAIRY RINGS
With the recent rains across the state, mushrooms and fairy rings have been showing up in home turfgrass lawns and athletic fields. Mushrooms showing up randomly in turfgrasses are the result of the rotting of organic matter (tree roots, tree stumps, construction debris, etc.) Producing the fruiting body that we see and call mushroom (or "toadstools"). When the mushrooms appear to form a circle in the turf they are known as the "fairy ring" fungal disease.
There are 3 types of fairy rings appearing in turf:
Type 1: Those that kill grass or badly damage it.
Type 2: Those that stimulate grass by forming rings of dark green turf.
Type 3: Those that do not stimulate grass and cause no damage, but produce mushrooms in rings.
The most common and destructive rings are the type 1 variety. They are the result of old tree stumps and roots, or construction debris rotting below the soil surface. The type 1 ring is distinguished by 3 zones; an inner lush zone where the grass is stimulated and grows luxuriantly; a middle zone where the grass may be dead; and an outer zone in which the grass is stimulated. The size varies from a few inches to several feet across. The stimulated zone is the result of the breakdown of organic matter, which releases nitrogen that stimulates the growth.
Mushrooms of the fungus causing the type 1 ring are produced in the bare zone or at the junction of the bare and outer zones. The fairy ring may be broken when it encounters a barrier, such as a large rock, pathway, or unfavorable soil condition. Rings get their start often as a cluster of mushrooms noted after heavy rains or an irrigation.
The dead areas of the fairy rings are brought about from the hydrophobic (water repelling) character of the mycelium that accumulates there. Thus, the grass dies not directly from the fungus killing it, but by keeping water from reaching the roots. In essence the grass plants are killed by droughty conditions in that zone.
What to do to control these unsightly rings? There are 3 approaches that can be considered: suppression, antagonism, and eradication.
Suppression is the easiest and most practical approach. This involves the core aeration of the area to allow for better water penetration, the use of wetting agents in the bare areas, and the optimal maintenance of water and nitrogen in the affected zone.
Antagonism is based on the premise that when fairy ring soil is mixed with other healthy soil, antagonistic organisms will suppress the pathogen. This involves the removal of the sod or the killing off of the area with a non-selective herbicide, then rototilling in several directions to completely mix the soil. Then prepare the soil as would normally be done for seeding or sodding.
Eradication, the final method, requires the most work, is expensive, and not always successful. This involves digging out all the infested soil in the ring and discarding it. The depth is usually down to 12 inches and about 24 inches on either side of the ring, to be sure all infested soil has been removed. Then the excavated area must be refilled with fresh soil, and either reseeded or sodded.
NDSU Extension Horticulturist and Turfgrass Specialist