Take heart! Natural enemies stalk weeds

Canada thistleBy Michael Leach

Weeds are villains in the garden story. They combine the reproductive prowess of a locust plague, kill resistance of a mad-slasher and relentlessness of sci-fi storm troopers. 

“Resistance is futile,” they are telling me. Looking in horror at the Amazon jungle growth threatening to take over the house, I’m inclined to agree.

But not just yet. Besides the inevitable late-summer slow down in growth, there’s news that offers a degree of moral support in the meantime. 

Weeds get sick. Take Canada thistle — puh-leeze (but wear heavy gloves when handling). Some are victims of a bacteria that makes them look bleached and so reduces their food making ability. According to The Ohio State University Extension, the bacteria, Pseudomonas syringae pv. tagetis, “cuts down on their seed head production and occasionally kills the plant. Laboratory-made extracts applied to thistles reduces seed production … by 87 percent. But this isn’t enough to overcome seeding by surviving plants.” No silver bullet.

Bugs eat weeds.  The mis-named tree of heaven, Ailanthus altissima, is the primary host  of ailanthus webworms. These little darlings can defoliate one of those odious and highly invasive trees. But so far, they are failing to stop the pest’s spread.

Another insect, a Southeast Asian import, also relies on tree of heaven as its main food source. But the spotted lantern fly, Lycoma delicatula, also dines on 70 other plants. Woodies are preferred but grapes, soy beans and other food crops are on its menu. 

It was discovered in eastern Pennsylvania in 2014 and is being monitored.

monarch and milkweedGood weeds face problems. Common milkweed, which can be weedy due to its underground assault, force roots and wins our hearts. It’s a food source for Monarch butterfly larvae. It’s garden-worthy flowers have an enticing fragrance and attract a wide range of pollinators, not just Monarchs.

Turns out it, too, has enemies, such as milkweed yellows, spread by leaf hoppers. The bugs suck juices from infected plants and spread them to healthy ones. Leaves curl and turn somewhat yellow, according to the Nature Scoop newsletter from Franklin Soil and Water Conservation District here in central Ohio. 

Obviously spraying to kill hoppers is problematic. 

The best management approach is removing infected plants to help stop the spread. That’s what I do with victims suffering aster yellows and garden phlox that dares to mildew. Out to the curb in a brown bag. 

The newsletter also carried encouraging news: Monarch Watch predicts the eastern Monarch population will increase this year due to favorable weather conditions. According to the Ohio Department of Natural Resources,  Monarchs migrating up the Atlantic coast appear to be from Florida not Mexico.

 

 

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