THE KEY TO HEALTHY BIRCH TREES? WATER
It may well be impossible to eradicate leafminers, so the tree needs to stay strong
Q I need some urgent help and was hoping you could provide me with some advice. We have birch burrowers and we don’t want to lose our tree, but an arborist is just too expensive. Do you have any suggestions on a solution — preferably something natural — that will get rid of the pests? If not, is there anything else that could possibly help?
A I assume we are talking about the birch leafminer. We have addressed this issue in the past, but it may be time to revisit the problem. A few years ago I received an email from Scott Digweed at the Northern Forest Centre, Natural Resources Canada, about birch leafminer. Here is what he said:
“I would suggest that eradication of birch leafminers is not possible here, nor is it a reasonable expectation in any biological control context. When new species are introduced, populations are brought under control either by native enemies attacking the new hosts, or by introduced enemies brought over from the host’s home environment to effect control in the new one. Once host-parasitoid relationships are established in the new environment, populations of the host and parasitoid will fluctuate relative to each other, but very rarely does one disappear altogether.
“I would not personally recommend treating birch trees chemically for birch leafminers. Topical chemicals or root drenches will affect parasitoids and predators, as well as the leafminers, which dilutes the chemicals’ usefulness. All birch leafminer species found in significant numbers here attack birch later in the summer, once leaves have provided much nutrient value to the trees already. The leaves don’t look great, admittedly, but I suspect the effects of the leafminers on overall birch health are negligible. Water stress is a much more significant issue for birch in the urban environment. Their shallow roots must compete with lawns for water. We used to recommend mulching under birches out to the dripline to help mitigate this stress.”
In other words, I’m afraid there is little that can be done. On a slightly more positive note, the City of Edmonton states, “Since 1990, populations of a tiny wasp (Lathrolestes luteolator) which selectively attacks the most damaging birch leaf mining pest (Profenusa thomsoni) have developed and drastically reduced the problem in the Edmonton area.”
While the statement says the problem has been significantly reduced it does not say that it has been eradicated. My best advice to you is to keep your birch trees well watered. Using a mulch may help to keep the soil moist, but watering regularly is the best bet. Birch trees have very shallow roots so they dry out quickly, and if they are allowed to dry out regularly it will damage them. You want the tree to be at optimum health to deal with the birch leafminer problem.
Q I’m curious as to what is the proper way to deadhead my petunias. I always thought that you could just pull out the dead/dying flowers. My mom insists that you also break off the end of the stem that it grows out of. Which is the best way to ensure I get the most blooms from my plant?
A You should know that mom is always right, and that is true in this case as well. If you just pull out the dead or dying flower you are simply cleaning up the plant and not really deadheading. If you look closely, behind that spent flower is a seed pod, and if you allow your petunia to keep producing seed pods without removing them the plant will think that its job is done for the season and begin to shut down production of flowers. This is the main reason so many gardeners complain that by mid– summer their petunias look burned out. Reach in behind that spent flower and remove the seed pod by pinching off the stem. On another note, my email inbox is overflowing with questions. This may be the most questions I have received since I started writing for the Journal over 30 years ago. Thank you for all your emails, but I ask for your patience as I try to get to them. I will try to answer every email, but if I don’t reply directly please look for your answer in an upcoming column.