Hi - Contacted you last late summer of asparagus concern. I have 5-15' rows...
Hi - Contacted you last late summer of asparagus concern. I have 5-15' rows of asparagus - 5 years old from crowns. After I stopped picking and about 3 weeks later last season (my 2nd year of harvest) I applied some nitrogen - dumb move I researched out. Within a week or so I had half my patch experience Bonzie growth of new spears - short bushy growth from newer spears or older ferns - I did not focus on where they were coming from but were low to the ground and a dark green. Left the ferns over winter as your site suggestes and removed early spring and burned. Spears appeared 2.5 weeks ago. I've harvested these last 6 days. PROBLEM: I've been only able to harvest maybe 20% of the spears at a height of 6 to 8 inches in good eating shape. The rest were very deformed? Shepards hooked bad, tops of spear eaten, very pale and wilted, MULTIPLE HOLES in wilted spears. I do have some nice spears I've picked but most now are pencil lead size and buds are starting to open on these at 2-3 inches in height. Many nice size spears are budding 2-3 inches above ground so I'm picking before they fern out. I am snapping off all spears regardless of size and height if they look about to fern out. Asparagus Aphids? What should I do for the rest of the picking season and after to save my patch!!!!!
Beltrami County Minnesota
The symptoms you have described suggest that aphids (as you surmised) and asparagus beetles are damaging the plants.
The following websites describe the life cycles of these pests and recommend ways to deal with them.
Asparagus Production Guide: Pest Management
The Benefits of Insecticide Use: Asparagus
Under the circumstances, remove the ferns in the fall rather than waiting until spring.