Slime flux (also known as wet wood) is a dark, foul-smelling and unsightly seepage of sap from tree trunks (fig. 1). The disease is not usually a serious problem but the appearance can be alarming. Slime flux is caused by common surface-inhabiting bacteria or yeast fungi that enter the trunk through wounds associated with improper pruning, stem breakage, injections, cracks from freeze injury or weak limb crotches. The bacteria and yeast may live on sap nutrients within injured trees for many years without any outward evidence. Symptoms The main symptom is the appearance of the dark sap oozing on the trunk exterior which happens when gasses produced by growth of the bacteria and yeast cause the internal pressure of the sap to become high enough to force the sap out through cracks in the bark. The dark streaks usually turn light gray or white upon drying. Oozing sap may be[Read More…]
Needlecast Diseases: Not Just a Spruce Problem
Many are familiar with Rhizosphaera needlecast of spruce. If you aren’t, please see these two articles by Janna Beckerman and Megan Haas for more information about the disease and it’s management on spruce. The common name for the disease, needlecast, describes the ultimate fate of the needles: they are cast off. Loss of leaves or needles hurts some trees more than others (Figure 1, 2, 3). Deciduous trees can tolerate some leaf drop each year with little harm, but conifers put a lot of energy and resources into making their needles, which remain on the tree for 2-5 years in most species. Some pine trees hold onto one or two years of needle growth while other pines and many other conifers retain their needles for much longer and rely on them to produce food, which is why if they fall off prematurely it can lead to decline and/or death of[Read More…]
Gray Mold of Bedding Plants
Gray mold (causal agent = Botrytis cinerea) is one of the most common diseases affecting bedding plants. Host commonly include (but are not limited to): begonia, carnation, chrysanthemum, cyclamen, geranium, impatiens, marigold, million bells, petunia, vinca and zinnia. Fortunately, gray mold is one of the easiest diseases to manage. By changing cultural conditions that are unfavorable to fungal growth, the disease can be successfully controlled. Symptoms and Signs The proper diagnosis is necessary prior to undertaking any control strategy. Because gray mold affects numerous host plants, care must be taken in examining affected plants. Symptoms of gray mold depend upon the type of host and the type of environmental conditions. Commonly observed symptoms include: bud blast, leaf spots, flower blight, stem canker, and/or crown rot, with plant death resulting (Fig. 1). Infected tissue is soft and brown, and may appear water-soaked. A key sign of Botrytis infection is the proliferation[Read More…]
Foliar Nematodes
Earthworms are not the only wigglers in the soil beneath your feet. Nematodes, microscopic roundworms, can be found in soil across the globe (even Antarctica!) and are often a barometer of soil and environmental health. However, the nematodes we encounter more frequently feed on plants and cause us, as plant stock producers and consumers, a ton of headaches. One subset of the plant parasitic nematodes that stands apart from the rest are the foliar nematodes (Aphelenchoides spp.). Unlike the vast majority of nematodes which strictly inhabit roots and soil, foliar nematodes (as their name suggests) live in and feed on leaves, stems, and buds. They enter the plant through stomates, natural openings for gas exchange in the leaf surface. As they feed, symptoms of foliar nematode injury appear as water-soaked lesions that eventually turn brown over time. With a broad host range of more than 700 different plant species, symptoms[Read More…]
Black Knot Disease
Black knot, caused by the fungus Apiosporina morbosa, is a recurring problem on Prunus species. Most Indiana fruit growers, both professional and amateur, have at one time or another observed the black, knot-like warty growths (Fig. 1) that often occur on the woody parts of plum and cherry trees. This fungal disease is one of the most common stone fruit problems in America. It infects both wild and cultivated forms of cherries and plums, and occasionally peaches; however, in general, plums are more severely attacked. The disease occurs routinely on wild cherry trees. A small swelling first appears on a twig or branch of a susceptible tree. Newly formed “knots” are greenish and soft but become hard and black with age. The growth enlarges every season, weakening the tree, and eventually it may completely girdle the infected branch. Trees severely affected by the disease are difficult to save (Fig 2).[Read More…]
Epidemiology Plant pathology is the study of plant diseases
Plant pathology is the study of plant diseases. In my career, I’ve studied or witnessed the plant disease epidemics of chestnut blight, Dutch elm disease, sudden oak death, soybean rust, and many more. I am not comparing these to the current pandemic of Covid-19. It doesn’t compare. Please understand this is just an opportunity for education. Epidemiology is the study of disease. It is a study by public health experts, and it is a study done by plant pathologists. There are some similarities and obviously, some very significant differences. Quarantines actually began in the fourteenth century in response to the Black Death (plague, caused by the bacterium, Yersinia pestis) and continue to be used to this day because they are effective. Quarantines and social distancing during the 1918 ‘Spanish Flu’ pandemic were implemented differently between Philadelphia and St. Louis, with very different outcomes (Fig. 1). A critical lesson from data[Read More…]
COVID-19 Guidelines for the Green Industry from Purdue Extension Specialists
COVID-19 will force the green industry to balance plant health and public safety.
Nootka falsecypress Dieback Problems
This Nootka falsecypress (Chamaecyparis nootkatensis) is showing severe dieback throughout much of the tree (fig. 1 and 2). The primary pathogen present is a fungus in the genus Diplodia. Small twigs are infected first, which eventually leads to dieback of larger branches (fig. 3). Note the spherical black spore bearing structures (pycnidia) at the base of needles shown in fig. 4. The dark spores (fig. 5) are spread by wind and splashing rain to other areas where they start new infections. Little research has been done on the diseases of falsecypress in the mid-West but the fungus appears to causing damage similar to problems it causes on other conifers, such as Austrian pine (https://www.purduelandscapereport.org/resource/diplodia-tip-blight-of-two-needle-pines/). Nootka falsecypress is native to coastal areas of the Pacific Northwest where they get abundant rainfall and have moderate summer temperatures. This specimen was growing between a sidewalk and a parking lot and had been through[Read More…]
Diplodia Tip Blight
The dead lower branches in these Austrian pines (Fig. 1) are due to Diplodia (= Sphaeropsis) tip blight. The causal fungus infects newly elongating shoots, in late spring, resulting in stunting and death of the new growth (Fig. 2). Black spore-bearing structures of the causal fungus are formed at the base of the stunted brown needles and on infected cones (Figs 3 and 4). Austrian pines are very susceptible to the disease, and infected trees often lose ornamental value as twigs are killed year after year. For more information on this disease, refer to BP-24-W, which can be found at: https://www.purduelandscapereport.org/resource/diplodia-tip-blight-of-two-needle-pines/
Impatient for new impatiens!
A workhorse of the shade garden, impatiens, also called ‘Busy Lizzies’ delight people by their amazing ability to brighten up shady sites. Downy mildew, caused by the water mold Plasmopara obducens put a damper on things for almost a decade. This downy mildew infects impatiens (Impatiens walleriana), or balsam impatiens (Impatiens basamina). New Guinea impatiens and other bedding plants are not susceptible to this downy mildew (but they may have their own downy mildews). Downy mildew quickly spread across North America, and impatiens were falling down on the job in landscapes. Symptoms begin with discolored leaves coated with white mildew on the underside (Fig. 1) consisting of sporangia (Fig. 2) that spread via wind, rain and wind-driven rain. As the pathogen colonizes the plant, leaves discolor and defoliate, leaving a lot of naked, green stems (Fig. 3). Summer weather that is rainy with cooler temperatures is conducive to impatiens downy mildew[Read More…]
