iGrow Gardening: Questions from area gardeners

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By David Graper

SDSU Extension Horticulture Specialist

Dead leaves on small apple tree

Q My small apple tree has lots of dead leaves all over. (See photos.) I sprayed it twice with copper fungicide thinking it may be fire blight, but it is getting worse. The tree is only 10 years old or so.

A I believe that you are correct in your assumption that this is fire blight, a bacterial disease, or another canker of some sort. Treatments with bacteriacides that contain copper can help to reduce initial infections, particularly during bloom, but will not cure an existing infection. Your pictures do not show the base of the stems with the brown leaves very well, but the closer image certainly shows that the twig is brown and dead. examine the twigs with the brown leaves to see if the twig is discolored, dark brown or almost black looking. You should be able to see a portion of the twig, closer to the main trunk, where the leaves are still green, and the twig looks a normal color as well. The tip of these stems will often exhibit what is called a shepherd’s crook with the tip bent over and those leaves all brown to black, like they were burned.

The wet spring weather that many folks had was conducive to the disease spreading from one branch to another in the same tree or between trees. Infected branches will ooze live bacteria that can be spread by the wind, rain or bees during bloom time. Hail damage or pruning cuts that have not yet “healed” can also be entry points for the disease.

At this stage, you can try to prune it out, during dry weather. Make your cuts on the infected branches at least 6 to 8″ below any sign of the discoloration. Soak your pruners or pruning saw in a Lysol solution or rubbing alcohol between cuts for a few minutes, so that you do not spread the disease further. However, this kind or pruning may just delay the inevitable. If this is a susceptible variety, it will very likely come back. And, if it finally gets into the main trunk, the tree will die.

Check out this article on recommended fruit varieties for South Dakota (http://igrow.org/up/resources/06-3001-2012.pdf) and this publication from the University of Minnesota Extension (https://extension.umn.edu/fruit/growing-apples-home-garden) for more information on growing apples, including disease management.

Small rhubarb stalks

Q After a spring of hard picking I have one rhubarb plant with many small stalks. (See photo.) While my other plants also have some small re-growth there remains some larger ones. Should I care about this condition and if so what should I do?

A It is very important to remember that when you harvest from a rhubarb plant, you are removing leaves, along with the stalks, actually called petioles. The leaves are used by the plant to manufacture food, in the form of carbohydrates (sugars) that are used by the rest of the plant for all of its energy needs. If too many of the leaves are removed, the plant can be weakened because its energy reserves have gotten low. The plant then does not have enough energy to produce nice large leaves and petioles right away again, until it starts to build up its carbohydrates again.

So, from what you have stated, I think you over-harvested and have weakened the plant. Do not harvest any more from these plants until you get a good amount of larger leaves and petioles again. Think of the leaves as solar collectors for the plant. The plant needs those to recover from harvesting. You would have the healthiest plant possible if you did not harvest at all. But of course, the reason we grow rhubarb is for harvesting. So, in the future, do not remove more than about 1/4 to 1/3 of the leaves and petioles at one time and then do not make another harvest until about the same number of leaves have regrown. If you notice that the petioles are getting pretty small again, stop harvesting for that season. You might also try incorporating about 1/2 cup of a 10-10-10 fertilizer into the soil around each large plant to give it a nutrient boost as well. For more information see: http://igrow.org/gardens/gardening/rhubarb-is-in-season/.

Above the ground gardening

Q Due to tree roots invading the garden, I can no longer plant tomatoes deeper than 6 inches. I am considering planting them in pots, but I don’t know the dimensions of a container that would be large enough to grow tomatoes. Also, wondering about what sort of soil to use in the pots.

A I would suggest the container hold at least 5 gallons of potting media. A larger container would even be better, since it help prevent the plant from drying out too quickly, making it less prone to blossom end rot. You can use a 5-gallon bucket if you wish, but drill some holes in the bottom to allow for excess water to drain out. I would suggest you use a pre-packaged potting mix. I have also seen mixes designed for use in raised beds that would work well. Do not just use soil from your garden — it likely doesn’t drain well enough and can contain pathogens, weed seeds etc. that can be a problem.

I would suggest you look for dwarf varieties for containers. There are quite a few of these available now. Some might say they are “patio” tomatoes. Typical tomatoes can grow too large, will tend to flop over if not carefully caged or staked and require too frequent watering to be a good match for this type of growing situation. If you do a little searching on the internet, you will likely come up with a number of suggested varieties to try. Or look in a gardening catalog for suggestions.

Bad soil

Q I’ve lost some perennials and shrubs lately and when I dig them out I find the soil is like gumbo. I don’t want to plant new things in the hole and use the same gumbo around them. Would using only Miracle Grow potting soil to plant the new things be okay or would I need to mix it with some new dirt other than the gumbo/clay?

A It is usually not a good idea to replace the soil or even mix in amendments when planting trees and shrubs. The plant’s roots will tend to stay in the new growing media you have created and not grow out into the existing soil around the planting hole. You would be essentially be creating a “pot” of new growing media, with the existing soil acting as the sides of the pot. That amended or replaced growing media will almost always be wetter or drier than the surrounding soils, so the roots will not likely develop as they should. The key is to look for plants that can tolerate growing in that kind of soil. We always suggest matching the plant to the site. Keep in mind that the roots of woody plants often will extend out at least as far as the plant is tall. So, you would have to change a major section of soil in your yard to be really effective.

Instead consider creating a raised area where you want to plant, using the same soil. That will increase the drainage and available oxygen for the roots and likely allow the plant to grow better.

Barnyard grass

Q I’m fairly sure barnyard grass is what’s showing up in my lawn especially along the driveway and sidewalk areas. Is it an annual and the plants will not return next year except for new ones or can it be treated with something now without harming the rest of the lawn? I’ve been able to pull some out when we’ve had rain but others are more difficult to get the roots. Would using crabgrass preventer in the spring have stopped it from germinating? Also, I was wondering if I used a crabgrass preventer in the spring would I be able to use the grass clippings in the garden and around other perennials and shrubs to hold moisture and hold down weeds?

A I think you may actually have crabgrass in your lawn. It is a more common weed than barnyard grass but they are both annuals and have coarser texture, so it could be either one. (See photo.) Barnyard grass is usually easier to pull than crabgrass since it doesn’t tend to sprawl out along the ground and root down at the nodes. Crabgrass has a much finer seedhead than barnyard grass as well. But, if you are keeping it mowed, it probably will not produce any flower heads. The crabgrass will readily flower even when mowed fairly short. The seedhead of barnyard grass is similar but much coarser with larger seeds that are easily felt when you rub your fingers over the seedhead. Each spikelet also has a little awn on the end of it so it will feel more bristly. Compare the two pictures below to see which one is a better match.

You could try a post-emergence crabgrass killer, but it is getting a little late in the season. Once the plants start to spread out along the ground and produce flower heads, they become much more difficult to control. Look for a spray that says for crabgrass, it will likely contain the herbicide quinclorac. Although I am not sure they will work on barnyard grass, because it wasn’t on the label that I was able to find. So, check the labels to see if it is listed there as a weed it will control.

The good news is that the typical crabgrass preventers that you would apply in the spring should control both kinds of weedy grasses. We normally apply these about the time lilacs start blooming in your area. Then they will be effective until the early fall. Since both of these grasses are warm-season grasses, they do not start to germinate until we have had a few weeks of warmer weather to warm up the soil.

I was not able to find anything on the label that indicated that you could use the clippings as mulch in the garden. You could potentially see some damage to your vegetables through root uptake of the herbicide. Check the labels of the products you can find in your area for more information on that particular question.

Curled tomato leaves

Q A gentleman is having trouble with his tomato plants with oddly curled leaves. (See photo.) It’s located on the north side of his garage in a bed that he’s planted random stuff in over the years. He lives in the middle of Wall, S.D. I was wondering if you think it’s some kind of fungus, virus, or just herbicide drift? The rest of his tomatoes look fine, so it seemed weird that this one is not doing well. I forget what variety he said it was. Bush Boy sounds familiar, but I’m not sure. Any thoughts on what this might be?

A This plant is exhibiting pretty classic symptoms of exposure to a small amount of a phenoxy type herbicide like 2,4-D, Banvel or one of the other broadleaf weed killers. The most actively growing parts of the plant are going to be most susceptible to damage, so that would be the upper parts of the plant. But it does seem odd that just that plant is showing the symptoms. Check other broadleaf plants, particularly potato, ash trees or grapes, if there are any growing nearby the tomatoes, and look for damage on those. Did anyone nearby apply any of these products? Any aerial spraying in the area? Keep in mind these herbicides can directly drift for a quarter mile or more and if it volatilizes, it can travel even farther.

Were the tomatoes mulched with grass clippings from a lawn that was treated? Any compost used that may have had manure from animals that fed on pasture or had straw that might have been treated? We have found out that even after going through the digestive tract of an animal some herbicides can still show activity. And in some cases, even when manure has been composted for several years. It is possible that this particular plant just happened to get some compost or grass clippings that had some residue on them. However, there is a leaf curl virus that could be the culprit as well. It can just affect one plant like that.

If drift is suspected from a neighbor’s field and the person who had their garden or land drifted on, they have the right to file a complaint. It should be made within 30 days of the application or the first appearance of damage (the sooner the better, preferably within days of the application). The complaint is made through Ag Services, South Dakota Department of Agriculture. They can be contacted at 605-7734432. A pesticide complaint can be filed on line at www.state.sd.us/eforms/secure/eforms/E2093V1-PesticideComplaint.pdf.

I cannot recommend that you eat the fruit from these plants, particularly if they are still showing symptoms on the new growth. However, the plants may grow out of it. But, there are no safe established levels for the consumption of fruit from plants damaged by these herbicides. So, to be safe, purchase tomatoes this year, or have the person that did the spraying purchase them for you.

The seeded of crabgrass looks like fingers pointing upwards. iGrow photo
Potential fireblight infected apple twig. iGrow photo
Barnyard grass plant and seedhead. iGrow photo
Weak vs. vigorous rhubarb petiole. iGrow photo
Suspected herbicide injury. iGrow photo
Potential fireblight infected apple branches. iGrow photo