ISSUE 7 June 15, 2000
HERBICIDE INJURY IN CORN LOW HERE
Recent reports from Illinois have shown corn injury from the herbicide Aim. This new postemergence corn herbicide was first registered in the United States in 1999. Low cost and effectiveness on such weeds as velvetleaf has allowed this PPO (portoporphyrinogen oxidase inhibitor, like other herbicides with this mode of activity (Authority, Blazer, Flexstar, Cobra), to be used. If injury is seen, it will usually occur within hours following the application and will show tissue chlorosis and necrosis on the corn plant. This "burn" look on the crop is due to rupturing of plant cell membranes.
Five years of research on this chemical through several states has shown that this herbicide can show corn injury ranging from 0-30% following postemerge applications. The symptoms usually seen are the necrotic lesions and in more severe cases breakage of leaf midribs on some of the leaves. Symptoms usually do not persist over 30 days after application.
This year in Illinois, the symptoms not only showed the classic leaf "burning" symptoms but also showed a tight wrapping of the uppermost leaves. This "buggy whipping" will usually be outgrown by the plant, but not on all the plants this year in Illinois. This year the more severe damage may be due to one of several speculated causes including: applications to wet corn foliage (dew or precipitation shortly after application) may have concentrated the chemical in the corn whorl; the plant may not have been able to metabolize the herbicide quickly enough; application with a crop oil concentrate (COC) not under dry conditions generally needing the use of the COC; or, tank-mixing Aim with another emulcifiable concentration (EC) herbicide with the total mix applied during environmental extremes. See the complete article from Illinois and pictures of damaged plants at: http://spectre.ag.uiuc.edu/cespubs/pest/articles/200011j.html.
CHECK YOUR SOYBEANS FOR NODULATION
Soybean plants that are six to eight inches tall should have their
first unfolded leaflets (V2 stage). Nodulation, the symbiotic relationship of bacteria on
the soybean roots, can be seen shortly after emergence, but the plant is not actively
fixing nitrogen until the V2 to V3 stages. The number and nodules formed on the soybean
roots along with the amount of nitrogen fixed increases until the R5.5 stage. Nodules
actively fixing nitrogen for the plant are pink or red inside. White, brown or green
nodules indicate that nitrogen-fixation is not occurring. Nitrogen fertilization after
planting (other than pop-up or early, limited fertilization) is not recommended as
nitrogen fertilizer applied to active nodules will render these nodules inactive or
depending on the amount of nitrogen applied. Soil nitrogen is utilized over fixed nitrogen, if available in large amounts. Check the health of your soybean nodules and check root proliferation. At V2, soybeans should be rooting down six inches into the soil and by V5 will completely reach between 30-inch rows, making any cultivation at V5 needing to be very shallow.
SATURATED SOILS AFFECT CROP GROWTH
Recent heavy rains and in some locations hail, like in Grand Forks,
Walsh and Pembina counties, have caused flooding, ponding, and plant damage across low
field areas. Prolonged soil saturation affects crop growth and yield. Corn is very
sensitive to flooding in the early vegetative stages (especially prior to the fifth or
sixth leaf stage). In early growth stages, corn or soybeans can survive for only two to
four days under water in anaerobic conditions. Moderate water movement can reduce flood
damage by allowing some oxygen to get to the plants, keeping them respiring and alive.
Drainage within one to two
days increases the chance of survival.
The injury extent to seedlings is determined by the plant stage of
development at ponding, duration of flooding and the air/soil temperatures as well as if
auxillary buds are present on damaged plants. If temperatures are warm during flooding
(greater than 77 F), plants may not survive 24 hours. Cool temperatures may prolong
survival. However, cold, wet weather favors disease development. Seed treatments are
effective, but limited in protection. Seedling development slowed or delayed two to three
weeks allow soil-borne pathogens a greater opportunity to cause damage. Seed rots, seedling blight, corn smut and crazy top affect corn plant development later even though ponding occurred earlier. Delayed soybean growth allows diseases such as Fusarium root rot, Phytophthora rot and Pythium rot to establish and weaken or destroy seedlings. Limited hybrid and variety resistance to these diseases and difficulty in predicting damage makes evaluation difficult. Carefully assess damage before deciding to replant or before tearing up the existing stand. The National Crop Insurance Service in their corn loss instruction booklet have shown that yield loss from early season stand reduction (up to the 10-leaf stage) can vary. With a 100%
plant stand, yield loss is negligible; a 75% stand can equate to a 10% yield loss; a 50% early corn stand is at least a 26% yield loss; and, a 25% stand will usually result in at least a 43% yield loss if original seeding rates were reasonable and remaining stands were healthy. In soybeans, research through various areas of the United States have shown that yields are not affected by population reductions until stands drop below 125,000 plants per acre but yields can be lower if large gaps are present. These skips can rapidly reduce yields in soybeans. According to information from Purdue, two-foot skips in soybeans in 50% of each row can decrease yield 6%. Three-foot skips in 50% of each row will drop yields 13%. Four-foot skips in 50%
of each row will decrease yield by 15% in healthy stands.
Rotted seed or damped-off seedlings will reveal probable crop losses. Evaluate intended stand to the damaged stand, the uniformity of the stand, the original planting date versus a replant date, likely replant pest control and seed costs as well as projected crop prices. Weigh these costs and price projections against replanting yield gains to evaluate crop injury and replanting gains.
On surviving stands, remember that favorable weather for plants after ponding is important. Cultivation, once soils are dry enough, will open and aerate surface soil and promote root growth. Be careful working the soil. Working wet soil causes compaction that varies crop growth.
An additional nitrogen application in corn may be necessary in fields that show signs of yellowing or uneven growth. A late test for nitrate when corn plants are still six to twelve inches tall can determine if more nitrogen is needed.
Scout more intensively in previously ponded areas of corn and soybean fields. Maintain a good weed control program so that crop plants are not robbed of nutrients and moisture later in the season.
Denise A. McWilliams
Extension Crop Production Specialist
APPRAISING HAIL INJURY TO SMALL GRAINS
Hail was reported yesterday June 6 and 7 in parts of North Central and North Eastern North Dakota. Prior to jointing hail most often has a minimal effect on yield; however, as the crop approaches reproductive developmental stages, injury to the growing point is more likely and leaf damage or loss has greater impact on yield.
Destruction of leaf area on young plants is seldom as serious as appearances may indicate. During early development the growing point is below the soil surface, making it less susceptible to injury. With this protection, small grains can suffer loss of above ground foliage without dying. If the growing point of small grain is not damaged the plants will likely recover.
When hail causes damage, it is advisable to wait several days after the injury occurs to make an accurate determination of injury. After this period, new growth on plants with uninjured growing points can be observed. If no regrowth is observed, the stem of the plant may be split to inspect the growing point. The growing point should be white or cream colored. Darkening or softening of the growing point usually precedes plant death. When the growing point moves above the soil surface at jointing in small grains it is vulnerable to damage.
Wheat and barley typically produce seven to nine main stem leaves. When leaf injury occurs at the three to five leaf stage most tillers have at least two leaves that have not emerged and are undamaged. The flag leaf, the last leaf produced on each tiller, is the most important leaf; if it remains undamaged throughout the growing season the yield potential will remain largely intact.
When severe injury from hail occurs to small grains after jointing plants still have the potential for recovery by initiating new tillers. Precipitation that usually accompanies hail storms will help stimulate tillering. Potentially, tillering can restore yields to acceptable levels.
Additional information can be obtained from NDSU Extension bulletin A-934, Replanting After Early Season Crop Injury. This provides excellent information on evaluating injury, however, this late in the growing season replanting is probably not advisable. Much of the crop in areas affected was probably not injured beyond the point of recovery.
Small Grains Extension Agronomist
HAIL DAMAGE IN OILSEED & ROW CROPS
Hail damage to crops occurs somewhere in the state every year. Reports have already been made last week and this week of hail in some 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. At this time its too late to consider a replant. Corn: The growing point remains below ground 2-3 weeks after the plant emerges (5-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. Corn in the silking and tasseling stage when damaged by hail can result in severe yield losses.
Soybean and Dry Bean: The growing points of beans are located
in the top of the plant and in leaf axis. 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. For dry beans one can get down to two plants per foot of row and still get 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.
Canola: Plantings in seedling stages can have stands reduced
by ½ and still produce acceptable yields. An average stand of 11-12 plants/ft2
can be reduced to 4/ft2 before yield losses exceed 10 percent. Prior to bolting
and flower development, canola can withstand hail without much economic loss. Canola with
leaves that are torn and shredded suffer only partial loss, while leaves bruised on the
main vein or torn and broken will be lost. Leaf area destroyed will result in seed yield
loss. Seed yield
losses in canola is approximately 25 percent of leaf area lost. If leaf defoliation is 50 percent, then yield loss would be approximately 12.5 percent.
Canola plants injured in late bolting or early flowering stages
seldom die. The well developed root systems and ability to rebranch and develop secondary
flower clusters help the plants recover. When buds or flowers are destroyed, the canola
recovers rapidly by development of flowers which normally would have aborted. New branches
also develop from growth buds lower down on the plant. Seed yield loss will depend on both
percent leaves and branches lost. For example, if canola has 60 percent lost branches 7
days into flowering, seed yield loss is estimated at 18 percent, whereas 21 days into
flowering, yield loss would be an estimated 60 percent. If hail strikes late, such as during pod filling or ripening, plant recovery is not possible. The time needed to develop new growth, flowers and mature is limited before a killing frost. Canola seed yield loss if injury occurs at the ripening stage depends directly on the loss of branches, individual pods and seeds knocked out of pods. Severe hail losses have occurred in canola swaths.
MAN-DAK ZERO TILL TOUR
The Manitoba-North Dakota Zero Tillage Farmers Association are sponsoring their annual summer tour on Tuesday, June 27, 2000. The tour will travel to South Dakota and visit the Dakota Lakes Research Farm at Pierre, SD. Host at the research sites will be well known SDSU Agronomist Dr. Dwayne Beck. Observe what he preaches:
Rotations - Sanitation - Competition. He also has some demonstrations on both dormant seeded canola and hard red spring wheat.
Bus transportation is being provided and can be boarded at two locations on June 27 which include:
6:00 a.m. - Holiday Inn Riverside in Minot, ND
8:00 a.m. - K-Mart Parking lot, 2625 State Street on Highway 83 in Bismarck, ND
All times are central daylight savings time.
To ensure a seat on the bus you must reserve in advance.
Before June 20-call: Alan Ness 701-530-2079
Bob Bradley 204-727-5355
After June 20-call: Alan Ness 701-530-2079
Following the tour, Bobs Steakhouse in Gettysburg, SD will be the final stop before returning to points of departure.
Duane R. Berglund