PLH is a sucking insect which excretes a toxin while feeding which stunts alfalfa plant growth. As a result, relatively low numbers of PLH are capable of reducing alfalfa yield. Significant PLH infestations may affect the following year's plant growth.
PLH passes through multiple generations per year. Both the adult and immature nymphs are important in causing injury and accurate identification is essential for assessment of potential injury.
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The treatment threshold varies with the height of alfalfa, since small plants are more susceptible to PLH than larger plants.
If the number of PLH collected per 10 sweeps is greater than the height of the alfalfa stand expressed in inches, then corrective action is warranted.
In addition, one should consider the following:
1. Stand stress (dry conditions may lower threshold).
2. Effect of current weather conditions on sampling.
3. Value of stand in relation to cost of treatment.
Ambush* @ 0.1-0.2 lb a.i./A
Baythroid* 2 @ 0.8 to 1.6 fl oz/A
Furadan* 4F @ 1 to 1.5 pt/A
Imidan 70WP @ 1.4 lb/A
Lorsban* 4E @ 1 to 2 pt/A
Mustang* @ 2.4 to 4.3 oz/A
Pounce* 3.2EC @ 0.1-0.2lb a.i./A
Sevin @ 1 lb a.i./A
Warrior* 1CS @ 1.92 to 3.20 fl oz/A
* Use is restricted to certified applicators.
If stand height is 16 inches or more, early harvest should be considered in place of treatment. However, regrowth should be monitored since PLH impact is greatest on initial growth.
Early harvest will reduce significantly PLH activity. If stubble treatment is required, time should be allowed for sufficient regrowth (3 or 4 inches) to hold treatment residue.
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