Bad “worms”

Iowa State University Extension gardening experts answer questions on damaging worms:


Worms are devouring the needles on my mugo pine.  What should I do?


The “worms” that are eating the needles on your mugo pine are the larvae of the European pine sawfly. European pine sawfly larvae are grayish green. Two light stripes and one dark stripe run down the sides of the body. The legs and head are shiny black. 


The larvae feed mainly on mugo, Scotch and Austrian pines, though other pine species are occasionally damaged. They do not feed on spruce or fir. Larvae typically appear in mid to late May in Iowa and are usually gone within a few weeks. 


European pine sawfly larvae feed on needles produced in previous years. (The needles on most  pines persist for two to five years.) They do not harm the new needles developing on the branches. As a result, the damage is mainly aesthetic. Larval feeding does not destroy the affected branches. The branches simply have fewer needles than normal. 


To keep damage to a minimum, the larvae of the European pine sawfly can be controlled by pruning off and discarding infested branches, knocking the larvae off affected branches into a bucket or other container and destroying them, or spraying them with an insecticide, such as Sevin. 


I occasionally find small, white worms in my cherries.  What is the best way to control them?


The small, white “worms” are probably the larvae of the cherry fruit fly (Rhagoletis spp.)  Cherry fruit flies lay eggs on developing cherry fruit in May. Damaged fruit appear shrunken and shriveled when ripe, and usually contain one off-white larva (maggot) that is slightly longer than one-quarter of an inch.


Cherry fruit fly damage varies greatly from year to year. It may be more practical to tolerate some damage and loss of usable fruit than to attempt effective preventive control.


To prevent maggots from appearing inside the fruit, the tree must be thoroughly sprayed with a labeled insecticide when the adults emerge and before the females lay their eggs inside the young fruit. Because the flies emerge over an extended period of time, several sprays will be needed. You can monitor fruit flies with yellow sticky traps hung in the tree in early May. Check traps daily after the first fruit fly is caught and repeat the spray application until flies no longer appear. 


Check for home orchard sprays and other insecticides at your local garden center. Carefully read and follow label directions.





2 Responses so far »

  1. 1

    berne Thury said,

    My japanese black pine has been invaded be (Ithink) a grub. grey/green in color with black stripes down back and black head and legs. I noticed it on the lower branches. They are eating the new growth. I sprinkled diazinon grandules over the area , then over the whole tree. They fell off and since most of the grandules fell to the ground as well , they died. Now can you tell me how they infected my tree? It is in it’s third season in my yard I mulch it heavily with wood chips yearly , that I get from the free wood chip pile provided by the Minneapolis park dept.
    Will they come back ?
    I also have a problem with green aphids on some impatiens that are in planters under a lindon tree. I plant them this way every year,and I’ve never seen an aphid on an impatiens before. Can you tell me why and how do I get rid of them? Thankyou sincerely Berne Thury

  2. 2

    Cindy said,


    I try to avoid strong chemicals as much as possible. For a more nature-friendly aphid spray, use 2 teaspoons of liquid Ivory dish soap per quart of water. Spray directly where you see the aphid infestation. Repeat every five days or when you see more aphids.
    Ladybugs are voracious aphid eaters. The beneficial ladybugs can be purchased at many garden centers. Don’t use the spray on the ladybugs, however, as it would affect the ladybugs.


    Also, the Linn County Master Gardeners offered this advice for your questions:

    Re: aphid control – Usually easy to control if they aren’t protected by tightly curled leaves, galls, or cottony material. Use an insect spray that has your infected plant listed on the label – make sure that it is safe to use it on that plant. Use a concentrate to quickly knock out existing aphids – such as Ortho bug-B-Gone Multipurpose Insect Killer concentrate. Aphids may continually reinfest the garden from other plants nearby. Inspect your plants regularly for aphids.

    As far as the “tree” problem – our Master Gardener who is the expert will be here Thursday pm. We’ll run it by him, then give you an answer. I hope this helps, and thanks for the questions.

    Bev Lillie
    Master Gardener Coordinator

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