The two tree health questions everyone has been asking this late spring are:
A visit to the Connecticut Agricultural Experiment Station in New Haven helped towards providing answers to these two questions.
White Pine Decline. A recent report by Dr. Nick Brazee of the University of Massachusetts summarized his observations regarding the condition of many white pines throughout southern New England. On many of these trees, the needles, especially the older needles are turning tan or yellow and otherwise showing the symptoms of a needlecast disease. Affected trees are widespread throughout the landscape and throughout the region.
In this report, Dr. Brazee identifies four fungi that are associated with this condition, 3 of which are fairly well-known in the region and a 4th, Septorioides strobi, that is a newcomer. However, Dr. Brazee suggests that it is not so much the presence of the fungi that is causing the problem; the trigger is the weather conditions over these past couple of years, especially the very dry conditions of 2015.
In the Plant Diseases Information Office at the CAES in New Haven, the findings of Dr. Yonghao Li and Ms. Lindsay Patrick are generally in concurrence with Dr. Brazee’s summary. The same disease fungi have been found in this state, including Septorioides, identified in CT last year. Yonghao and Lindsay also agree that the weather patterns of the past couple of years have a major role to play in what is occurring.
However, the PDIO cautions that there still may be more to the story. For instance, the weather patterns throughout New England have shown local variation. As one example, while last June was very wet in much of New England, it was still relatively dry in southern Connecticut. Also, symptoms of needlecast have begun to show up on this year’s needles, suggesting lingering effects that might go beyond just last year’s weather.
In fact, this general issue of ‘white pine decline’ has been under discussion in New England for the past several years, as shown in a 2012 pest alert from the US Forest Service on white pine damage.
Dr. Li and the PDIO office is very interested in hearing further from arborists from around the state concerning their observations regarding the conditions on eastern white pine. Besides the needlecast diseases, PDIO would be interested in whether other diseases are becoming more noticeable, such as pitch canker, a pine disease that affects the bark, branches and other parts of the trees.
Meantime, Dr. Li recommends people look to Dr. Sharon Douglas’s excellent guide, Disease Management Guide for Connecticut Arborists 2015-16, available through CTPA’s website. A printed version of this publication is also available through the CTPA office.
People who wish to contact the PDIO may visit the PDIO website (www.ct.gov/caes/pdio) or call 203-974-8601.
Diagnostic services are also available at CAES’s Valley Lab in Windsor. That office may be contacted at 860-683-4977.
Gypsy Moth. About now, people in the south-central and eastern parts of Connecticut are beginning to ask – what is going on with the gypsy moths? For many, this question is a refrain from last year, when many of those same parts of the state witnessed defoliation due to gypsy moth on an order not seen for several years. The number of gypsy moth caterpillars that people are noticing this year – hanging from branches, scattering frass over car hoods and roofs and showing up on people’s clothing after working outside – are a direct consequence of the dry spring and early summer of last year. The question for this year is whether the intensity of last year’s outbreak will be repeated.
Dr. Gale Ridge in the Insect Information Office at CAES suggests that the situation will be much better this year than last. The missing actor in 2015, which Gale expects to return in full force this year, is the maimaiga fungus. Last year’s June rains came too late and even then, not everywhere, to adequately derail the 2015 outbreak. As a result, we had significant defoliation in much of the state last year, with enough gypsy moths surviving to adulthood and reproducing to set the stage for this year.
The key to all if this is moisture, or its absence, especially in the leaf litter. Moisture triggers the fungal resting spores of maimaiga in the leaf litter to release, while the high local humidity helps the growing fungus to penetrate the larval insect’s cuticle. In the later instars, especially the 4th and 5th instars, the gypsy moth caterpillar becomes a commuter, as Dr. Ridge’s describes it, stopping feeding during the heat of the day to seek cooler temperatures at base of the tree. As they do this, while in the leaf litter, a certain number of the caterpillars will contract the fungus and die as they climb back up the tree, their bodies bursting open to release conidial spores that can directly affect other gypsy moth larvae. These conidial spores are short-lived but, towards the end of the gypsy moth larval period, the fungus switches to producing the persistent resting spores that can begin the control of future generations of gypsy moths.
Dr. Ridge expects that people in areas with high numbers of gypsy moths can expect to see the characteristic hanging cadavers of fungal-killed gypsy moth larvae within the next 10 days or so. While some has already occurred, it is normally in the last two instars that the greatest damage is seen. Gail, along with most of the rest of us, is hoping that this will not happen, as the maimaiga fungus stops the fungus in its tracks.
For a very good, pre-maimaiga overview of the gypsy moth life-cycle, see the Gypsy Moth Handbook.