4 keys to effective aphid management in leafy greens
In order for vegetable growers to successfully compete in the new market, they need to produce high-quality, pest-free crops. This is especially challenging for leafy growers, where the damage caused by aphids can drastically reduce yield and quality.
In many areas where lettuce is produced, aphids are an economically important pest found in the crop.
Types of aphids
Many aphid species infect and damage leafy vegetables. Among them, the green peach aphid, Mycelium persica, is generally the most notable because of its wide host range, the tendency to pesticide resistance, and the tendency to infect plants rapidly. Other species such as the foxglove aphid, the algae Solani, and the lettuce aphid, Nasonovia ribisnigiri are important aphid pests of lettuce in the western United States.
Due to their small size and high reproductive capacity, aphids are often undetected until they grow to the point of damage.
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How aphids cause damage
Aphids pierce the leaves through the mouthpiece like needles and feed by removing plant sap. Excessive feeding by infectious diseases can inhibit plant growth, and some aphid species can divert viruses that are pathogenic to many leafy vegetables. However, they are economically important because of the contamination of harvestable plant material (e.g. lettuce heads, celery hearts) by aphids. Contaminating leafy vegetables with a few aphids will often reduce the quality or make the product unpalatable.
4 keys to controlling aphids
Because aphids have the potential to quickly contaminate plants, it is important to prevent their installation in order to produce quality crops. Here are several management tips that farmers can consider when dealing with aphids on leafy vegetables.
1. Start with prevention
Potential aphid problems can sometimes be avoided with preventative cultural practices.
Destroying crop residues immediately after harvest will reduce the spread of aphids to nearby crops. Aphids are also abundant in weeds, so proper hygiene and complete weed control of the crop and its surroundings can help prevent aphid formation and spread.
Natural enemies, common female beetles, lacewings, syphilis flies, and many other parasitic wasps, can help suppress aphid populations affecting leafy vegetables. Cultural practices such as planting "subsidiary crops" (e.g., alisum) that protect and promote natural enemy populations may also help prevent aphids from colonizing crops.
Cultural management and natural enemies cannot always prevent aphid colonization, and pesticides may be needed to prevent contamination.
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2. Scout Fields Complete
In anticipation of aphid infestation, farmers should start searching as soon as the stand is established. Focus on the airy edges of the fields. Infections are most often found on the edges of fields near the prevailing wind direction. Aphid colonization begins with the movement of females with a few wings into live nymphs. Many of these offspring turn into mature, wingless aphids, and they deposit live nymphs.
Nymphs that do not have these wings are the ones that cause problems in polluting. Infections can develop quickly when the weather is favorable, and fields should be searched frequently, at least two or three times a week.
When sampling aphids, it is important to inspect the entire plant. The distribution of wingless nymphs within plants varies among aphid species. In lettuce, green peach aphids colonize old frame leaves, whereas foxglove and lettuce aphids can deeply affect young terminal plant growth in heads or hearts. Understanding the distribution of aphids will also help identify them.
3. Aphid identification is important
When winged aphids initially begin to spread into the growing area, they move from crop to crop until they find a host suitable for colonization. However, the presence of winged aphids in lettuce or celery crops does not mean that you should expect aphid infection to eventually develop.
In Western America, for example, small grains (e.g., corn leaf aphid) or alfalfa (e.g. pea aphid), but not lettuce, are often found in lettuce plants in the fall. After determining that aphids spinach with these wings is not an acceptable guest, farmers do not need to worry about them moving and controlling them.
Proper identification can save farmers money and prevent unwanted pesticide applications.
Once wingless aphids are found to be colonizing plants, aphid identification can also be important in determining control measures. Pesticide performance in the field will vary from product to product, but will vary depending on the species of aphid you are targeting.
For example, neonicotinoid pesticides can be very effective in controlling lettuce green peach aphids using a foliar spray (Acyl 30sg, Acetamibrid, United Phosphorus Inc.) or soil application (Admiral Pro, Imidacloprid, Bayer Crop Science). However, the same pesticides are generally not very effective against foxglove and lettuce aphids. Some aphid species are naturally less susceptible to certain types of pesticides.
4. Use pesticide sprays in advance
When aphid infestation cannot be prevented by cultural practices and natural enemies alone, pesticides can be a reliable option to control pests. Research shows that leaf pesticides are most effective at the beginning of aphid colonization or, in particular, when the presence of some wingless nymphs is first detected in plants. In glacial lettuce, it is recommended to use foliar sprays based on the nominal range of action; Sprays should be started when there is at least one aphid colony (four to five nymphs) sampled on average 10% of lettuce plants.
The fields should be re-sampled for five to seven days following spraying and re-treated if the threshold is violated. This approach reduces the use of pesticides and improves the protection of lettuce heads during harvest. This method is also used successfully in other leafy vegetables.
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