So this week I will do a piece about wire worms and root knot nematodes (RKN). some how since running this piece several years ago the wire worms have ceased being the problem they once were. But the RKN have more than filled the void. RKN are and will always be a work in progress.
Good morning, in my garden are two
pests that could easily drive one to distraction. Research and the
developing of a game plan for their control is critical. They have
conflicting garden cultures. These two critters are root knot
nematodes (RKN) and wire worms ( larvae of click beetles ).
Both of these critters affect plant roots but do it in different ways. With RKN the females enter the root but remain close to the outer layers of the root where the males have access.. The female remains within the plant depositing eggs while the young leave the host plant to enjoy other plants. It is the egg laying that gives these lovely critters their name. Laying eggs forms galls (knots) on the roots. Light infestations and the plant continues growing but with less vigor. Severe infestations can disrupt the plants ability to take up nutrients and can then lead to the death of the plant. As for wire worms, they have a tendency to feed on roots and tubers. As a rule of thumb only seedlings die from wire worm infestations (eat all of the seedlings roots). What wire worms do best is to chew little 1/16 of an inch diameter holes into the sides of tubers and roots, such as sweet potatoes, Irish potatoes, carrots and beets. They do not kill these plants but these superficial wounds diminish or eliminate the tubers sellabilty. These wounds are superficial and is only a visual thing. Edibility is not affected..
One of the real culture difference for these two pests deals with the use of compost. With RKN it is recommended to add compost to help thwart them. The theory is to encourage bacteria and other soil borne critters that have an affinity for RKN. I have noticed that this does work in reducing RKN populations. On the other hand, with wire worms, I have read numerous accounts that show reduced compost in the soil will help thwart wire worms. It wasn't until I read the logic behind this cultural treatment that I feel it has validity. Wire worms are drawn to an area with higher CO2 gas concentrations. Normally this would be from the germination or other growing activities of plants. Well compost passes a lot of gas, no pun intended as it decomposes. Kinda like a red cape and the bull charges. But this can be used to the disadvantage of wire worms too. We will get to this.
Another discrepancy between these two critters is the use of any of the grass family. Cereal rye, Secale cereale ( not rye grass, Lolium multiflorum) is a trap crop for RKN. I am not exactly sure how this trap crop works. I see two possibilities, one where both sexes enter and nobody leaves including the young. The other where only the female enters and does not have access to males or if she does the young cannot leave. Anyway it diminishes the population of RKN. Click beetles thrive in grass lands ( My garden is surrounded with native grass lands, my source of these critters). They prefer eating on grass roots, especially wheat ( most likely rye to). This crop can be used to draw the wire worms to the germinating seedlings and away from the crop. The grass can then be pulled and disposed of along with any wire worms that are attached to the roots ( chickens say YUM, for both greens and larvae). With RKN the rye is merely mowed down and tilled in. The RKN are killed when the rye decomposes. Now for some real conflict in cultures. If the rye is used for RKN control, it would be unwise to plant any of the above mentioned tubers and root crops as a succession crop in any of the RKN rye beds. The wire worm population would have easily exploded since they thrive in grass. Now for the kicker wire worm larvae take anywhere from 2 to 5 years to mature. It is for this reason that I do not see myself using rye to combat RKN. On the other hand I might use it to draw wire worms away from my sweet potatoes or Irish potatoes. I have not noticed any carrot or beet wire worm infestations. The rye bait could be a strip of rye planted on both sides of sweet and Irish potato plants the length of a bed. Then once the soil heats up to 60 degrees (temp where wire worms become active) these seedlings could be pulled and then disposed of accordingly.
Another cultural practice that is affective for RKN but not for wire worms is bed solarization. This is where a plant bed is thoroughly watered, graded very flat, covered with a clear plastic film and all edges are buried to trap moisture and heat. When done in May and June temperatures of 130 to 140 degrees to a soil depth of 6 to 8 inches can be achieved. It can really fry RKN. Not so with wire worms. Once the soil begins to warm above 85 degrees the wire worms migrate down into the soil profile where the soil is cooler. Once the soil cools down below 85 degrees in the fall they resume feeding. This is why on a sweet potato tubers you will see larger healed over holes and smaller unhealed holes. Spring feeding and fall feeding. With this info, harvesting tubers as soon as they are of size in mid to late August would circumvent this second feeding because the soil would be above 85 degrees.
And now for one last different treatment. Cold pressed raw neem oil (CPN) has different affects on these two pests. Studies have shown that CPN hinders and suppresses RKN. Wire worms on the other hand, are repelled by CPN . It is recommended to spray every 14 days to continue diminishing RKN and to also continue repelling wireworms.
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