Asparagus Beetle Infestation
- 3 year old asparagus bed - problem first noted today, 05/16 - ferns affected, at least one crown had shepherd's crook - noticed fewer spears than usual about a week or two ago - had thought they might just be late in emerging. at least one crown has had no spears yet this year. - full sun location - soil a bit dense/clay-ey, do add black earth and/or mulch w/ newspaper as weed suppressant each year - no pesticide or fertilizer applications - fern debris is usually left all winter I am fairly sure of my pest diagnosis of common asparagus beetle: adult beetles are orange/black with 4ish cream spots. Larvae are gray with black heads. Severely affected ferns are yellowing with blunted ends. As mentioned before, spear production much less than previous year. Questions: Are beetles to blame for diminished spear emergence this year? Best methods for larvae/beetle elimination/reduction besides hand removal?
Diminished spear production could be due to several factors. If you had beetles that damaged the foliage last year, that would reduce the plant's photosynthesis which could result in reduced spear production. Also, you mention that you do not fertilize. Asparagus is a medium-heavy feeder and requires annual nitrogen in late winter or very early spring. The dense soil could as be a factor in reduced production as well.
Take a look at our page on asparagus beetles and methods of controlling them.
https://extension.umd.edu/growit/asparagus-beetles-vegetables. Adding flowering plants to the garden helps to attract predators such as lacewings, lady beetles and tiny parasitic wasps that can help control these beetles naturally.
Also, here is our guide to growing asparagus:
http://extension.umd.edu/sites/extension.umd.edu/files/_docs/articles/GE100%20Asparagus.pdf. Do not leave the foliage over winter; cut it down after the first frost. This removes overwintering sites for pests.