LANDISVILLE, Pa. — At its most basic, crop farming is about producing more and better food plants — and weeding out the plants that interfere with that goal.

Attendees picked up ideas for both parts of that mission during Penn State’s Farming for Success field day on June 27 at the university’s Landisville research farm.

Jessica Williamson, a Penn State forage management professor, is working on increasing production of the good plants.

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Jessica Williamson, a Penn State forage management professor, speaks about interseeding alfalfa into corn.

With a team of researchers from other states, she is studying the process of interseeding alfalfa into corn.

The ideal planting time for alfalfa is early August. That gives the crop plenty of time to get established before winter sets in.

Of course, the corn is still standing in early August, and waiting till after corn chopping isn’t the greatest idea.

“After we harvest our corn silage, we have 100 other things that we need to get done, and planting alfalfa oftentimes falls to the bottom of the list,” Williamson said.

Those competing priorities can push alfalfa planting all the way to the spring.

Cover crops are usually interseeded when corn is around the V5 stage, but alfalfa can be interseeded earlier — after the corn is planted but before it emerges.

That means, instead of using a specialized interseeder machine, farmers can interseed alfalfa with a regular no-till drill, Williamson said.

The interseeded alfalfa generally straggles along until the corn is harvested. After that, it flourishes.

But after one year of data collection, the alfalfa also seemed to reduce corn yields by 7-14%.

The worst losses were in Pennsylvania. But the state also got by far the most rain of all the research sites, and it’s too soon to know how the cropping system will perform under less extreme weather, Williamson said.

Roundup Ready alfalfa provided an advantage over the cheaper conventional version when interseeded last year.

Being able to use glyphosate helped a lot with weed pressure, she said.

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Dwight Lingenfelter, a Penn State weed scientist, speaks about an herbicide trial.

While Williamson was talking about the good plants, weed scientist Dwight Lingenfelter was talking about a farmer’s foe — burcucumber.

The weed is nearly impossible to manage right before harvest, Lingenfelter said.

By that time in the season, the vine could be 20 or 30 feet long, and the corn will be so tall that any herbicide would need to be applied by highboy sprayer or aircraft.

Burcucumber vines tend to get tangled in machinery, so it’s best to go around them when harvesting.

Corn from a problem area is best chopped for silage, an early stage of the fall harvest.

When the burcucumber seeds are light green, ensiling will kill the seeds. More mature brown seeds can survive, Lingenfelter said.

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Tosh Mazzone, a Penn State research technologist, speaks about the tree of heaven.

Tosh Mazzone, a Penn State research technologist, has also been thinking about ways to kill another unpopular weed.

The tree of heaven, found in stream buffers, wooded areas and disturbed ground, was known as an invasive species long before researchers discovered that it’s a preferred host of a more recent invasive pest, the spotted lanternfly.

That finding has given landowners a new reason to control the tree, but it can easily be mistaken for desirable native trees.

The first step in controlling tree of heaven, then, is knowing what not to kill.

The invasive tree has compound leaves, meaning many leaflets are arranged around a single stem, Mazzone said.

Its bark is fairly smooth, and a broken stem lets off a rank odor.

“Some people tell me that it reminds them of peanut butter, or rotten peanut butter, or something really gross,” Mazzone said.

Black walnut also has compound leaves, but the edges of its leaves are sawtoothed. Its bark has deep grooves, and its wood is dark colored.

Walnuts lying on the ground below the tree are also a pretty good sign. The tree of heaven doesn’t produce nuts.

The shagbark hickory has compound leaves, but its leaflets are much larger and wider than the knifelike ones on the tree of heaven.

The hickory also produces nuts.

“Even if you didn’t plant it, it’s going to seed in because those birds like to eat them,” Mazzone said. “They’re going to drop the nuts all over the place.”

Perhaps the nearest lookalike to tree of heaven, sumac grows in clumps like the invader, but its compound leaves have a serrated edge.

Sumac produces bright red fruits in the summer.

Once it’s clear that a worrisome tree is in fact a tree of heaven, the landowner needs the right mix of technique and timing.

If the tree is sprayed or mowed in the spring or summer, the tree will just push more stems, leaving the extensive root system unaffected.

“In fact, it’s going to stress that tree probably so much that it’s going to send up more little baby plants all over the area,” Mazzone said.

It’s better to save tree of heaven controls — which include fire, mowing and herbicides — for later in the summer.

The ideal control period is from July till the leaves start to change color in the fall.

During this period, the tree is drawing sugars into its roots to prepare for winter. Herbicide applied at this time will be carried down into the roots as well.

When the tree is small or the infestation is large, a foliar herbicide can be used. A glyphosate-triclopyr mix is commonly used.

If sensitive crops are in the area, the trunk can be soaked from 18 inches down to the root flare in an even mixture of basal oil and triclopyr.

There’s also the “hack and squirt” method.

To use this, make several hatchet cuts near the bottom of the trunk, then use a spray bottle to put a glyphosate-water mix into each of the cuts.

“Doesn’t seem like much, but that’s plenty to kill one of these trees,” Mazzone said.

Just don’t cut the bark the whole way around. That girdling will stop the plant juices flowing to roots, and therefore stop the herbicides riding in them as well, he said.

Phil Gruber is the news editor at Lancaster Farming. He can be reached at (717) 721-4427 or pgruber.eph@lnpnews.com. Follow him @PhilLancFarming on Twitter.