Herbicide Injury Symptoms in Sugar beets
Don W. Morishita and Robert W. Downard
Herbicides are an important tool for controlling weeds in crops. Unfortunately, misusing them can cause problems. One of the most frequent problems associated with pesticide misuse is crop injury. Injury can be the result of herbicide carryover, herbicide drift, or misapplication of a registered herbicide.
Making an accurate diagnosis of crop injury based only on visual symptoms is difficult. Many factors besides chemicals can contribute to symptom expression. These include weather, nutrients, soil moisture, diseases, and insects. It is important to remember that injury symptoms from different sources can look similar.
This bulletin gives information for diagnosing herbicide injury in sugar beets. It shows injury symptoms caused by incorrectly applying herbicides currently registered for use in sugar beets. It also shows injury symptoms caused by drift and carryover of herbicides not registered for use in sugar beets, but commonly applied to crops grown adjacent to sugar beets or in rotation with them.
The publication gives general information on several herbicides, including their mode of action, and a description of their typical injury symptoms in sugar beets. Figure 1, Figure 2, Figure 3, and Figure 4 show normal sugar beet seedlings at different growth stages.
Many factors can contribute to crop injury, and crop injury often is the result of a combination of factors.
Herbicides registered for use in sugar beets
Betamix- This postemergence herbicide is absorbed through the foliage and does not translocate in the plant to any extent. It inhibits photosynthesis.
Typical injury symptoms from the cotyledon stage through the true leaves include chlorosis (yellowing) and necrosis (death) where the herbicide contacted the leaf. Leaf tip and leaf margin necrosis will appear as early symptoms (figure 5). Injury from applications made at temperatures greater than 85 F will generally appear as blotchy or spotted chlorosis soon after application; and necrotic spots may develop later (figure 6 and figure 7). If the injury is not too severe, the sugar beet will recover.
Eptam- Used as a layby treatment for weed control, Eptam is readily absorbed by roots and translocated upward to the leaves and stems. Its exact mode of action is not known, but is thought to be an inhibitor of cell division in the plant meristems. Typical injury symptoms include leaf malformation (figure 8).
Herbicide 273- This herbicide can be applied preplant or postemergence. Its specific mode of action is unknown, but it is known to disrupt cell membranes. It is also used as a desiccant in some crops. The injury symptom from a preplant application generally is leaf malformation along with some leaf chlorosis (figure 9). The typical postemergence application symptom is an immediate leaf burn followed by necrosis (figure 10).
Nortron- Can be used preplant incorporated, preemergence or postemergence. It is absorbed by the emerging shoots or roots of most plants when soil-applied. Foliar absorption is greatly reduced after plants have a mature cuticle. Nortron is translocated to the foliage following uptake by roots and emerging shoot, but is not translocated out of treated leaves.
Injury symptoms that appear at the cotyledon stage from preplant or preemergence applications include some leaf malformation and leaf tip burn (figure 11). As the seedlings get older, injury symptoms include a more pronounced leaf malformation with some petiole elongation, or narrow leaf blades and a very upright appearance (figure 12). Leaf development also may be retarded and the apical meristem (growing point) may appear reddish. Nortron can be applied postemergence, but only in combination with Betamix. Injury symptoms from postemergence overapplications include leaf burn, necrotic spots on the leaves, and sometimes a reddening of the growing point (figure 13 and figure 14).
Pyramin- Pyramin can be used preplant incorporated, preemergence, and postemergence. Absorption is primarily through the roots with very little through the foliage. It is a readily translocated herbicide, presumably through the xylem (water conducting tissue). Pyramin inhibits photosynthesis.
Injury symptoms from the cotyledon stage through the appearance of true leaves are very similar. The first symptoms are chlorosis and necrosis of the leaf tips (figure 15). As the sugar beets get older the chlorotic injury symptoms on the leaf may become slightly mottled or discontinuous.
Overapplication preplant or preemergence may delay or prevent crop emergence. Postemergence application injury symptoms include leaf chlorosis and necrosis as well as leaf thickening.
Ro-Neet- Ro-Neet is used as a soil-applied herbicide, although it can be absorbed through the leaves of plants, as well as through the roots. Because of its volatility (high potential to evaporate), it is not used as a foliar herbicide. It is readily translocated to the leaves after uptake by the roots. Ro-Neet apparently interferes with cell division in the meristematic regions (areas of active growth) of plants.
Typical injury symptoms of emerging sugar beets are cupping of the cotyledon leaves and the first true leaves (figure 16). Symptoms of larger seedlings include leaf malformation (figure 17).
Stinger- A postemergence herbicide, Stinger is readily absorbed by foliage and roots then translocated upward and downward before accumulating in meristematic tissue. It is a growth regulator herbicide. Its mode of action, causing abnormal growth, appears to be similar to that of phenoxy herbicides.
Typical injury symptoms are leaf petiole elongation and distorted leaf growth (figure 18). These symptoms are similar to 2,4-D injury symptoms.
Treflan- Registered for use in sugar beets as a layby herbicide, Treflan does not have the ability to control emerged weeds. Treflan is absorbed through the roots, and it is not translocated. It interferes with the physiological growth processes of germinating seeds and is thought to slow seedling growth by inhibiting cell division.
The typical injury symptom from lay-by misapplication is girdling at the root crown (figure 19). Treflan also is registered for use in several crops grown in rotation with sugar beets. Injury can occur from Treflan residue in the soil. The resulting injury symptom is stunted sugar beet growth (figure 20).
Non registered Herbicides
Assert, Harmony Extra, Matrix, and Oust- These herbicides have the same mode of action. They inhibit the synthesis of three amino acids produced in plants. Assert and Harmony Extra are registered for postemergence weed control in small grain cereals, Matrix is used in potatoes and Oust is used for noncrop weed control such as roadsides. All of these herbicides are translocated. Assert, Matrix, and Oust are moderately residual herbicides and can injure sugar beets by carry over in the soil or from spray drift. Harmony Extra is a short residual herbicide and does not pose a carryover problem. It can however, injure sugar beets from spray drift.
Symptoms of drift injury from Harmony Extra, Oust, and Assert are so similar it is not possible to distinguish among them. Symptoms include leaf chlorosis. Chlorosis can be followed by necrosis if the injury is severe enough. Injured plants will sometimes develop a very prostrate or flattened appearance (figure 21). If the plants are small, the leaves may be more erect. One way to distinguish the difference between Harmony Extra and Assert drift injury may be by observing the weeds in the field. Harmony Extra controls many different broadleaf weeds and no grasses while Assert controls only wild oat, some mustard weeds, and wild buckwheat.
Like drift injury symptoms, carryover injury symptoms of Assert, Matrix, and Oust can be very similar. Typical symptoms include narrowing and chlorosis. The leaves may also be somewhat erect (figure 22, figure 23, and figure 28). Depending on the location of the chemical in the soil, sugar beets may not exhibit symptoms immediately. If the chemical is buried in the soil, injury symptoms may not begin to appear until after several leaves have developed and the sugar beet root has grown down to the chemical.
Buctril and Bronate- Registered for use primarily in small grain cereals, alfalfa, corn, and some other crops, Buctril contains the herbicide bromoxynil. Bronate is a mixture of bromoxynil and MCPA. Buctril and Bronate are used for controlling broadleaf weeds.
Bromoxynil is not translocated very much once it is absorbed by the plant. It inhibits photosynthesis and respiration. MCPA is a growth regulator herbicide similar to 2,4-D symptoms (figure ?).
Drift injury symptoms from MCPA are very similar to 2,4-D symptoms. Typical injury symptoms from bromoxynil include leaf burn and necrosis. Bronate-injured plants often will have both symptoms, but depending on the extent of injury, one symptom may dominate. If the injury is severe, leaf burn and necrosis will be the dominant symptom (figure 24). If the injury is slight, elongated petioles (typical of a growth regulator herbicide) will be dominant.
2,4-D and Banvel- These growth regulator herbicides are registered for broadleaf weed control in many cereal crops such as wheat, barley, oats and corn. They also are used for roadside weed control. They upset the balance of natural plant growth hormones resulting in abnormal plant growth. Both herbicides are readily translocated through the plant.
Typical injury symptoms on sugar beets are elongated petioles and deformed leaves (figure 25). As plants begin to recover, new leaves may take on the appearance of celery stalks (figure 26).
Metribuzin and atrazine- Metribuzin (Lexone or Sencor) is used in potatoes, cereals, alfalfa, and several other crops. Atrazine is used primarily in corn and certain noncrop areas. Both herbicides can be used preplant, preemergence, and postemergence. They have some residual in the soil, which can present potential carryover problems to sugar beets.
Both herbicides inhibit photosynthesis. They are absorbed primarily through the roots, but can be absorbed through the leaves as well, and are translocated in the xylem.
Injury symptoms from carryover on sugar beets include leaf chlorosis and tip burn on the leaves (figure 27 and figure 28). As the injury progresses more of the leaves will exhibit necrosis. Metribuzin and atrazine are somewhat mobile in the soil and can move into the soil profile. If the chemical has moved into the soil, injury symptoms may not begin to appear until after several leaves have developed, when the sugar beet root will have grown down to the chemical.
Don W. Morishita is an Associate Professor of Weed Science and Extension Specialist at the University of Idaho Twin Falls Research and Extension Center.
List of Figures
1. Cotyledon leaves growth stage of normal sugar beet.
2. First true leaf growth stage of normal sugar beet.
3. Third leaf growth stage of normal sugar beet.
4. Normal sugar beet seedling approximately 7 weeks after planting.
5. Betamix injury on cotyledon leaves- leaf tip and leaf margin necrosis.
6. Blotchy chlorosis and necrosis from Betamix injury from application at high temperatures.
7. Necrotic spots from Betamix application at high temperatures.
8. Eptam injury- malformed leaves.
9. Herbicide 273 preplant application injury- leaf chlorosis and malformed leaves.
10. Herbicide 273 postemergence application injury- leaf burn and necrosis.
11. Nortron preplant application injury- malformed cotyledon leaves and leaf tip burn.
12. Nortron preplant application injury- narrow leaf blades and upright appearance.
13. Nortron postemergence application injury- leaf burn with necrotic spots and reddish growing point.
14. Nortron + Betamix postemergence application injury- leaf burn and reddish growing point.
15. Pyramin preplant application injury- leaf tip chlorosis and necrosis.
16. Ro-Neet injury at the cotyledon growth stage- cupped leaves.
17. Ro-Neet injury at the seedling growth stage- malformed leaves.
18. Stinger injury on a sugar beet seedling- elongated petioles.
19. Treflan layby application injury- root crown girdling (normal root at left).
20. Treflan carryover injury- stunted growth (normal plant at left).
21. Harmony-Extra drift injury- leaf chlorosis and flattened appearance (flattening does not always occur).
22. Assert carryover injury- leaf chlorosis.
23. Oust carryover injury- leaf chlorosis or reddening and erect appearance.
24. Bronate drift injury- leaf burn, necrosis, and elongated petioles.
25. 2,4-D drift injury- elongated petioles.
26. 2,4-D drift injury several weeks after initial injury- leaves resembling celery stalks.
27. Metribuzin carryover injury- leaf tip burn. Older leaves show symptoms first.
28. Metribuzin and Matrix carryover injury- leaf tip burn and erect leaves.