ISSUE 10 July 3, 2003
YIELDGARD‚ ROOTWORM HYBRIDS FOR ROOTWORM CONTROL
There was a great deal of press earlier this year with the EPAís approval of corn that was genetically engineered to control corn rootworm. This new technologies was developed by Monsanto and is being marketed as YieldGard‚ Rootworm. Seed of YieldGard‚ Rootworm was restricted this year and plantings were largely limited to the western Corn Belt where corn rootworms are the most pernicious. A commercial agreement between Monsanto and Pioneer was recently struck that will enable Pioneer to use this technology in their hybrids in the future. Next year we will no doubt see a range of hybrids with this rootworm resistance. Currently YieldGard‚ Rootworm hybrids are registered for use in more than a dozen states including South Dakota, but not yet North Dakota.
YieldGard‚ Rootworm hybrids contain a genetic modification, a Bt gene, that causes them to produce a toxin in the roots in sufficient quantity to kill rootworm larvae that feed on them. The development of this genetic modification has to be considered as a major technological breakthrough as farmers in the USA currently spend a billion dollars annually on insecticides to control corn rootworms. The YieldGard‚ Rootworm technology is similar to that used in Bt corn hybrids that have been grown widely in North Dakota for the past several years. The genes in both systems come from the same bacterium (Bacillus thuringiensis), though they do produce different toxins and in different parts of the plant. Should you use YieldGard‚ Rootworm hybrids in the future.
Initial data indicate that rootworm control is excellent with this new technology, in many cases exceeding that obtained with insecticides. Furthermore, this technology is integrated in the seed so there is no special equipment required and no handling of insecticides. Whether it will be profitable will depend primarily on the level of rootworm infestation that you have. Generally speaking, corn rootworms are not a problem in the North Dakota. Furthermore, corn rootworms even in more southern states build up to damaging levels only in continuous corn as the larvae feed almost exclusively on corn roots and will starve in their absence. There are some areas where the corn rootworm does not hatch during the soybean phase of a corn-soybean rotation (referred to as extended diapause rootworms), so in these areas a corn soybean rotation does not adequately control them (though a corn-soybean-soybean-rotation would). YieldGard‚ Rootworm hybrids only control rootworms, and will have no effect on white grubs and wire worms. A seed dressed insecticide will still be required for these pests. There are also some market restrictions for YieldGard‚ Rootworm corn; it canít be sold in the European Union, for example.
Growing YieldGard‚ Rootworm hybrids will be probably only be profitable in North Dakota -
The best time to assess the potential for corn rootworm damage next year is during a three-week period after pollination. When the adult population averages one beetle per plant in continuous corn or 0.5 beetles per plant in first year corn fields, the potential for larval root damage the next summer is sufficient to justify control measures (rotation, insecticides or YieldGard‚ Rootworm hybrids when approved for use in ND). Without the benefit of extensive research in North Dakota it appears that most corn growers in North Dakota will not routinely need this new technology.
Extension Agronomist Ė Cereal Crops
Heat injury to seedlings occasionally occurs on hot sunny days, with air temperatures in the range of 85_95 F and soil temperatures of 120 F have been recorded. Heat injury is commonly associated with drought injury, but excessive heat will also injure plants even if moisture is plentiful. We have experienced high temperatures in recent days which may have injured or reduced yield potential of this years canola crop in some regions of the state.
When in the blooming stages, heat blasting and or flower abortion is a strong possibility. This can vary from field to field and is very dependent on time of flowering, soil moisture and humidity during the hot periods. Usually in this situation one would see no or limited pod growth and thus no seed set. It will usually be in patches on the main stem and branches as related to time of flowers pollinating and the heat stress. With good soil moisture under canola usually flower abortion will be minimized to some extent.
Both low and high temperatures can adversely affect development prior to and during flowering. Low, but non_freezing, temperatures just prior to flowering slow the rate of plant development. The start of flowering is delayed or, if begun, the rate of flower opening is slowed and the amount of pollen shed is reduced. High temperatures at flowering will hasten the plant's development, reducing the time from flowering to maturity. High temperatures during flowering shorten the time the flower is receptive to pollen, as well as the duration of pollen release and its viability. This can decrease the number of pods which develop and the number of seeds per pod, resulting in lower yields. It appears that Brassica rapa (Polish) is more susceptible to this type of damage than Brassica napus (Argentine). Very hot weather combined with drought may cause bud blasting wherein the flower clusters turn brown and die resulting in serious yield losses.
Once pods are formed, canola is more tolerant than at flowering to high temperatures. Cool night temperatures at this time also help the plant recover from extreme heat or dry weather.
However, during this stage, a combination of heat and extreme drought will severely affect the pod and seed development including formation of seeds, seed size and oil content. The seed oil content is highest when seeds mature under lower temperatures (50 to 70 F). High temperatures during seed maturation result in reduced oil
content. High temperatures, drought and long days hasten maturity and in combination, can reduce yield through fewer pods, with fewer lighter seeds per pod.
OPTIONS FOR WET OR HAILED FIELDS
Too much rain to often in some eastern regions of the state. Severe hail in some areas with little chance of crop recovery. That was the bad news this past week. Wet weather or severe hail damage often forces abandonment of cropped acres. These acres often dry too late to grow a crop and salt accumulation on these acres could hurt future crops if a cover is not established this summer to use some of the subsoil water. Salts accumulate because of high water tables. Salts are harmful to crops because they produce drought in the midst of good moisture conditions. In 60 days a growing crop can use 4-6 inches of soil water and reduce the threat of salt buildup. It is important to check with a local county Farm Service Agency-USDA office to determine what crops could be grown as a cover. Sudangrass or a sorghum-sudan mixture would be an ideal cover and water using crop. Seeded at 12 to 15 lbs/acre, the seeding will destroy weeds through seedbed tillage and will germinate and grow rapidly. This rate is lower than the seeding rate for forage production. Before planting any cover crop, make sure that government program requirements are compatible with any planting plans. Also, one must determine were herbicides applied that will remain as residual and injure cover crop selected. Some type of tillage is also needed in the fall so that fields will dry next spring. Also monitor and spray for weeds that may become a problem with seed production and reinfest the abandoned fields.
SENSITIVE PERIOD FOR CEREALS
In the past week hot weather has resulted in very rapid growth and development of the small grain crop.
Most of the small grain crop is in the boot through flowering stages. The challenge this presents is, much of the small grain crop was not sprayed to control fusarium head blight (scab). Hopefully the hot weather will slow down some of the cereal diseases.
Boot through flowering are the growth stages when a small grain crop is most sensitive to stress. Moisture stress while in the boot will cause spikelets to abort. Moisture stress combined with high temperature results in even greater spikelet abortion. The most sensitive time is just prior to, and during flowering. Hot temperatures and high humidity during this time can kill pollen resulting in sterility. There have been some reports of barley and wheat heads turning white at the tips. When sterility occurs florets will open in an effort to intercept pollen making them more susceptible to certain diseases, particularly ergot.
Most have seen the readily visible effects of applying broad leaf herbicides during these sensitive growth stages. For example, growth regulators often result in curled/twisted heads and stems. What is not considered is the less visible effects of herbicide applications during sensitive times. These are the same as described for environmental stress, spikelet abortion and sterility.
Early boot through flowering are the sensitive stages, with the time just prior to and flowering the most sensitive. Remember barley flowers while in the boot just prior to head emergence while wheat flowers one to three days after head emergence. Any stress at these critical periods can reduce yields.
Duane R. Berglund
NDSU Extension Agronomist