| ||Weed control in barley | Barley diseases | Insect pests of barley
Weed Control in Barley
Weeds are responsible for serious yield losses in barley and controlling them will usually result in a substantial increase in net income. Weeds compete with barley for light, nutrients and moisture. When these factors are limiting, barley yields will be reduced. The yield reduction will be directly proportional to the weed population in the crop. In many areas of Alberta, yields are still reduced by 15 to 20 per cent through competition from weeds.
Wild oats constitutes a major weed problem to many barley growers in Alberta. Research on barley in central Alberta shows that yield losses through competition from wild oats may be predicted when the number of wild oat plants present per unit area is known. This is done by applying the equation:
L = 0.023 times A times square root of X
where L is the predicted yield loss (g/m2)
A is the predicted weed-free yield (g/m2)
X is the number of wild oat plants per square metre. (5.38 g/m2 = 53.8 kg/ha = 1 bu/ac)
If a field of barley would yield 322.8 g/m2 (60 bu/ac) with no wild oats present, but it is found to have 30 wild oat plants per square metre by actual count, then the predicted yield loss can be calculated as follows:
L = 0.023 times A times square root of X
A = 322.8
X = 30
therefore L = 0.023 x 322.8 g/m2 x sq rt of 30
L = 40.67 g/m2 (7.6 bu/ac) yield loss.
Weed seeds present in barley grain may be responsible for major dockage and grade losses at market time. Excessive weed growth present in barley harvested for silage may reduce the quality of the fodder and can affect palatability. Malting barley contaminated with excessive numbers of certain weeds will not achieve malting grades. The cost of control must be balanced by the expected increased return to the producer from an increase in crop production, both in the current year and in future years.
There are five fundamental methods of controlling weeds in barley.
Physical control measures
- Use weed free seed.
- Use only clean, weed-free machinery and hauling facilities.
- Restrict animal movement from weedy fields to clean fields.
- Handle weedy manure in a manner to eliminate spread of viable weed seeds.
- Where possible control or restrict wind and water movement from weedy to weed-free areas.
- Use a chaff collector on the combine to remove chaff and weed seeds for feed or processing
Cultural control measures
- Tillage that will bury weeds, expose them to frost or drying, or wound them to allow for entry of decay-causing
- Hand weeding of smaller patches of select weeds.
- Mowing where tillage is impractical.
- Burning weeds prior to maturity.
- Pasturing and grazing to prevent seed formation.
- Mulching small weed patches with clean straw, manure or polyethylene film.
Today, however, with the herbicides available, delayed seeding is a very doubtful economic practice for controlling weeds. Seeding fall-sown crops in rotation with barley is an effective weed control ,measure. Crop growth is established before weed growth begins in the spring.
- Use crop rotations that may include fallow, forage crops, row crops, or fall-sown cereals, to take advantage of weaknesses in the life cycle of existing weeds and thereby eliminate them.
- Plant competition. Any measure that enhances vigorous crop growth helps to control weeds. This can include increased seeding rates.
- Adjust timing of cultural operations. Delayed seeding has traditionally been used to control certain weeds.
Biological control measures
This technique has not yet been perfected to the point where it has any major value to individual barley producers. Control agents are usually insects or diseases which attack only one specific weed.
Chemical control measures
Many herbicides are available for use on weeds commonly found in barley in Alberta. Most herbicides, currently recommended, are relatively cost-efficient and are the only widely applicable means of controlling weeds in the growing crop. Care must be taken when using herbicides to rotate herbicide modes of action or use multiple modes of action as herbicide resistance is becoming a serious problem in a number of common weeds in Alberta. For more information, please refer to Herbicide Resistance in Weeds – Frequently Asked Questions.
When herbicides are used as directed, they usually do a good job of controlling a wide range of weeds, though some are specific and control only a few species. If there is weed misses, not easily explained by applicator error, consider the possibility of herbicide resistance and have the weeds tested.
Most of Alberta's fields have some wild oats resistant to group 1 or group 2 wild oat herbicides.
From a 2010 survey of Alberta the top ten weeds, in declining order in barley are wild buckwheat, wild oats, chickweed and Canada thistle, volunteer canola, dandelion, hemp nettle, corn spurry, cleavers and narrow-leaved hawk's beard.
Major diseases in barley are pathogenic in nature and are caused by fungi, bacteria or viruses. Other diseases are non-pathogenic and are caused by harmful environmental factors such as nutrient deficiencies or adverse weather. Pathogenic diseases are controlled most easily by using resistant varieties, but these are not always available. In some instances, the development of resistant varieties by plant breeders is nearly counterbalanced by development of new races of the pathogen. A good crop rotation with a mix of cereals, oilseeds, forages and/or pulses can greatly reduce the chance of disease affecting your barley crop. A short rotation or continuous barley cropping can quickly lead to a loss of resistance to disease.
Common root rot
Common root rot is the most important disease of barley in Alberta. Annual yield losses for southern and central Alberta, in the latest survey, were estimated at 10 per cent. Spores are present in the soil, germinate and invade plants just below the soil surface, infecting the crown and subcrown internodes. Infected plants tend to be stunted or lacking in vigor, and show brown discoloration of roots, stem bases, crown, and lower leaf sheath.
Seed treatments are most commonly used to prevent this disease from occurring. Shallow seeding also reduces the risks. Rotating barley or wheat with other non-cereal crops will reduce the number of spores in the soil, and consequently reduce root rot in the following barley crop; however, some spores do remain dormant for 2 or 3 years. None of the varieties available is highly resistant, but our best varieties are either moderately resistant or tolerant. Tolerance can mean it is susceptible but can tolerate fairly heavy infestations without yield loss.
Barley scald is a leaf disease that spreads and develops best in cool, humid weather frequently experienced in June and early July in the parkland area of Alberta. It can first be recognized by light green oval or lens-shaped spots on the leaves that quickly dry to white areas with brown margins. Yields are affected only when the top two leaves are damaged, as lower leaves do not contribute directly to grain filling. Average yield losses in the most recent survey were estimated at 2.4 per cent, ranging from negligible in census divisions 1 to 3; to 5 per cent in census divisions 11 and 12. Scald can be controlled by rotating barley with other crops because it overwinters on infected leaves. Good scald resistant varieties are available. The varieties with the highest resistance are Sundre and Gadsby. Many other varieties have moderate resistance.
Net blotch can be recognized by brownish streaks on the leaves that have a network of darker brown lines within them. Net blotch fungus overwinters on the seed or on crop residues in the field. It infects the foliage of the new crop and spreads most rapidly during warm and humid weather. There is both a net form and a spot form of net blotch. Like scald, it is usually most apparent at heading time and does not reduce yields unless it damages the top two leaves. The latest survey results indicate that net blotch caused an estimated 1.5 per cent yield loss in Alberta, with the heaviest losses in census divisions 5, 6 and 7. It can be controlled by seed treatment and crop rotation. Several varieties have moderate resistance to the spot form.
Barley stripe is a potentially very destructive disease that has been almost unknown in Alberta until very recently, probably because of the relatively high level of resistance in our varieties. The disease is seed borne and no effective commercial seed treatment is currently available. Use resistant varieties to avoid this disease.
Smuts are seed borne diseases. Loose smut, covered smut, and false loose smut are widespread in Alberta, but do not have much effect on yield over the province as a whole. Losses in individual fields can be significant and growers should ensure that seed planted is either free from smut, or treated with a recommended fungicide.
False stripe or barley stripe mosaic is a seed borne virus that occurs in Alberta, but has been kept under control. Symptoms closely resemble those of true stripe. The virus has no known vector and must be spread by plant contact. Thus, the only source of the disease is infected seed.
Barley yellow dwarf
Barley yellow dwarf is caused by an aphid-transmitted virus that frequently causes severe yield losses in California and the northwestern United States. Infected leaves turn golden yellow from the tips downward and infected plants are stunted. The aphids do not overwinter in Alberta so the virus must be re-introduced here each year by wind-blown aphids. The disease usually arrives too late to cause much damage. Late-sown spring crops can be severely infected, as well as fall cover crops.
Insect Pests of Barley
Damage from insect pests can usually be minimized by cultural practices and proper use of insecticides. Cultural control should be used wherever possible to reduce the need for insecticides. Use an Integrated management approach when dealing with insects. When insecticides are necessary to prevent loss, they should be applied with caution and only as recommended. With some insect pests, bad timing of insecticide can hurt the nature predators of the pest far more than the pest itself.
Wireworms are slender, hard-bodied, shiny, yellow worms, the largest about 2.5 cm (one inch long). Eggs are laid by adult beetles in the spring and larvae may remain in the soil for 5 to 10 years before pupating and emerging as adult click beetles in early summer. Populations build up slowly but fields remain infested for years if larvae are not controlled. Wireworms feed on germinating seeds and underground parts, shredding the stems but seldom cutting them off. Severe damage results in thin patchy stands. The central leaves die but outer plant leaves often remain green for some time.
Barley is more tolerant to wireworm damage than wheat or rye, but will be damaged when infestations are heavy, such as on new breaking of grassland. Current seed treatments do not kill wireworm but they are stalled in development. Shallow seeding into moisture and firm packing will effectively prevent damage when populations are low.
Cutworms are fleshy, soft-bodied worms that curl up and remain motionless when disturbed. Fully grown, they are about 3 to 5 cm (1.15 - 2 inches) long. The most common species are the pale western cutworm, most prevalent in grassland areas, and the redbacked cutworm, prevailing mainly in parkland areas. Both feed at night, cutting off plants just at or below the ground surface. Damage is most severe when plants are in the seedling or early tillering stages. Other less common cutworms include the dingy cutworm and the glassy cutworm.
Damage by cutworm species can be controlled by discouraging egg laying. Leaving summerfallow undisturbed during August to mid-September reduces egg laying by pale western cutworm moths which lay at this time into loose and dusty soil. The redbacked cutworm will lay in weedy fallow and weedy patches in crops, therefore, weedy summerfallow in parkland areas should be worked during this period. Young larvae of both species can be starved in the spring by destroying green growth 10-14 days before seeding. Because late seeding will result in lower yields, it is usually preferable to seed during the optimum time and use a chemical control if necessary for cutworm control.
Grasshoppers periodically can damage field crops, especially in dry years. There are three main pest grasshopper species, although a couple of others have become damaging. All over winter as eggs that hatch in the spring. Depending on species, eggs may be laid on roadsides or headlands, or scattered throughout stubble fields. Damage is most severe during dry periods in the early stages of crop growth. Relatively cool and moist growing conditions reduce grasshopper feeding and encourage crop growth, allowing the barley to keep ahead of damage. Seeding early and producing a vigorous crop assists in reducing damage.
Forecasts of the expected extent and severity of outbreaks are prepared jointly by Alberta Agriculture, Food and Rural Development; Agriculture and Agri-Food Canada; and local agricultural service boards. The forecast is posted on the Ropin' the Web website, under maps and multimedia and in most farm papers. When grasshoppers first hatch in breeding areas such as roadsides and headlands, they can be controlled by early applications of insecticides to these relatively small areas. Fall tillage helps to destroy eggs by exposing them to predators and the elements.
Aphids seldom inflict economic damage on barley crops in Alberta. Infestations do not normally build up to damaging levels until the crop is nearly mature. Damage occurs most frequently when barley is sown late in the spring or as a cover crop in the fall. If very heavy infestations build up (50 per plant) before heading, chemical control may be justified. Of the many species present, only 3 or 4 are of economic importance.
Barley thrips have damaged crops in westcentral and northern Alberta on rare occasions. Thrips feed on the developing head while it is in the boot stage, and first indication of their presence is the appearance of "white heads" in the field. Yield loss is proportional to the number of damaged heads, but the striking appearance of the white heads in the green crop leads to overestimates of damage. Control is not practical since the damage is complete by the time it is obvious in the field and thrips are not exposed for chemical control to work.