"News You Can Use"
May 2013
Fungal Diseases of Roses
Fungal diseases on roses begin as spring turns to summer - Roses, one of the most common landscape flowering shrubs, can be beautiful with lush green foliage and brightly colored flowers. Unfortunately, they are also vulnerable to a couple of very common fungal diseases, powdery mildew and black spot, which can turn plants slightly in a short period of time. Black spot is specific roses, but powdery mildew can occur on a wide range of landscape plants. As such, you may see disease on your roses, bedding plants, and turfgrass all at the same time. The specific fungus causing disease on each of these plants is actually a different fungal species, but the environmental conditions that favor disease is similar and plants may become infected at the same time of year.
Black spot requires leaves to be wet for several hours in order for spore germination and infection to begin. Secondary spread of the disease occurs when spores are splashed from infected leaves to uninfected leaves by rain or sprinkler irrigation. Powdery mildew, on the other hand, doesn't require free water on the leaf surface, but does require high humidity for spore germination and infection. Cultural practices reduce leaf wetness and humidity can be helpful in managing these diseases. For example, it is best to avoid wetting the leaves when irrigating. If this isn't possible, then plants should be watered early in the day so that the leaves dry quickly. Additionally, planting in sunny locations with good air circulation, avoiding overcrowding, and selectively pruning plants to open the plant canopy, will help reduce disease. When planting new roses, select disease resistant cultivars. Good fall sanitation practices are also important for an overall disease management program - rake and destroy fallen leaves (do not compost diseased plant material) and prune out infected canes. Lastly, many fungicides are available to help control these diseases. For best results, use early in the disease cycle before symptoms are too widespread or severe and be sure to completely cover the plant including the upper and lower leave surfaces. Contact: Natalie Goldberg
April 2013
Loose Smut of Wheat
Have you seen dark black seed heads on your wheat? If so, your plants may be infected with the fungus, Ustilago tritici. The disease is commonly referred to as loose smut of wheat. This disease has been known for centuries and is easy to recognize in the field. The disease appears at heading when dark brown to black, smutted, seed heads appear among newly emerged, healthy, green heads. The seed in these diseased heads are converted into a mass of dry, dark brown to black spores (teliospores). The disease is called loose smut because the spores produced on smutted heads are easily removed by wind and rain. Typically, after a short while, only the bare, sooty, flower stocks remain. In some cases, the seed head is only partially infected. Prior to heading, diseased plants may have dark green leaves with chlorotic streaks, but this symptom generally goes unnoticed. Seed with no visible symptoms can be infected with the fungus. Loose smut occurs worldwide. It reduces yield in proportion to the percentage of "smutted" heads. Although yield losses are usually less than 1%, losses closer to30% can occur under conditions that are especially favorable for disease development. In contrast to other wheat seed diseases, loose smut has little to no effect on grain quality for food or feed. More information on loose smut of wheat can be found on the Loose Smut Fact Sheet. Contact: Natalie Goldberg
November 2012
Black Rot on Butternut Squash
At the end of October, a butternut squash with classic symptoms on black rot was submitted to the NMSU-Plant Diagnostic Clinic or disease analysis. The fruit was incubated in a moist chamber and a few days later, Didymella bryoniae, was sporulating on the surface of the fruit. This pathogen is the causal agent of black rot. It is also the causal agent of gummy stem blight, a devastating disease of cucurbits in the field. Yield loss occurs from both pre-harvest and post-harvest losses. As a fruit rotting pathogen, Didymella bryoniae can be particularly damaging to winter squash (butternut, acorn, buttercup, hubbard, etc.) and pumpkins. Other cucurbits such as watermelon, cucumber, and grounds are also affected. The disease occurs worldwide in tropical, subtropical and temperate climates. It has also been reported in greenhouse production. More information about this disease can be obtained from the Black Rot of Cucurbits Fact Sheet. Contact: Natalie Goldberg
October 2012
Bacterial Leaf Spot Affecting Pumpkins in New Mexico and Texas
Recently, pumpkins from two different fields, one in New Mexico and one in Texas, were submitted to the New Mexico State University Plant Diagnostic Clinic for disease analysis. The fruit was exhibiting small, round, slightly sunken spots with tan to beige centers. On one of the fruits, spots were enlarging, becoming noticeably sunken, and the rind was cracked in the center of the lesion. Inside, the flesh was rotted all the way to the seed cavity. Infected tissue was plated for fungal and bacterial pathogens. No fungal pathogens were isolated, but pure cultures of Xanthomonas campestris pv. cucurbitae, the causal agent of bacterial leaf spot, were isolated from fruit from both fields. This disease causes sporadic losses in cucurbit crops grown in temperate climates. In New Mexico, the disease is not common, but can occur when warm, humid conditions are persistent. The disease attacks a number of different hosts including pumpkin, cucumber, gourds, and summer and winter squash. More information about this disease can be obtained from the Bacterial Leaf Spot of Cucurbits Fact Sheet. Contact: Natalie Goldberg
August 2012
Alfalfa Mosaic Virus on Peppers
Over the past month, the New Mexico State University - Plant Diagnostic Clinic has received several plant samples that are exhibiting severe symptoms of Alfalfa Mosaic Virus (AMV). This virus is found worldwide on a wide variety of cultivated plants and weed species, and is particularly common on plants in the solanaceous (nightshade) and leguminaceous (pea) plant families. It is common in New Mexico on chile peppers and has also been identified on tomato, bean, alfalfa, peanut, cowpea and lavender. While this disease occurs every year in New Mexico, it rarely causes serious economic losses as the number of plants infected in any given field is usually low. It can, however, severely infect individual plants resulting in little of no fruit production. Symptoms caused by Alfalfa Mosaic Virus can be somewhat varied, but the most common symptom is white to yellow blotches in a mosaic pattern on the leaves. Other symptoms seen in peppers include white discoloration that occurs in a ringspot or curving mosaic pattern. When young plants are infected, they are stunted and produce small, deformed fruit. When mature plants are infected, the fruit produced before infection is normal, but little or no fruit is produced after infection. More information on this disease can be obtained from the Alfalfa Mosaic Virus Fact Sheet. Contact: Natalie Goldberg
July 2012
Pink Root on Onions
Are your onions smaller than you'd like? Do the roots have a reddish-purple hue? If you answered yes to these questions, than your plants are suffering from a fungal disease known as pink root. Pink root on onions is caused by the soil-borne fungus Phoma terresstris. This pathogen is common in New Mexico and is problematic worldwide wherever onions are grown. The disease is especially devastating in warmer climates. Although many isolates of this fungus are specific to onion, some have the ability to infect other hosts including tomatoes, soybean, eggplant, pepper, spinach, carrots, corn, small grains, cucurbits, corn and ryegrass. The most noticeable symptom of the disease is the reddish-purple discoloration that occurs on infected roots (Figure 1). Roots of infected plants become dysfunctional and plants will suffer from nutrient deficiency and drought. When young seedlings are infected, they may die; however, death is not the end result when more mature plants are infected. In this case, plants are stunted, exhibit leaf tip dieback and bulb size is reduced affecting overall yield and marketability. More information on this disease can be obtained from the pink root fact sheet. Contact: Natalie Goldberg
June 2012
Entomosporium leaf spot
If you've noticed reddish purple spots on the leaves of your indian hawthorne or red tip photinia, your plants are most likely infected with a fungal disease known as Entomosporium leaf spot. This disease is common on plants in the rose (rosaceae) family, but is particularly problematic on indian hawthorne (Raphiolepis indica) and red tip photinia (Photinia fraseri). The disease is especially troublesome in locations were cool, wet springtime conditions prevail. In New Mexico, the conditions that favor disease development do not last very long. As such, this disease is usually fairly mild on plants grown in New Mexico. When infection is low or mild, the damage is cosmetic - the plants don't look good, but the overall health of the plant is not affected. The overall health of plants with severe infections is negatively affected. Heavily infected plants may prematurely defoliate weakening them to environmental stress, insects and other diseases. More information on this disease can be obtained from the Entomosporium fact sheet. Contact: Natalie Goldberg
August 2011
Common Corn Smut
Common Smut Appearing in Corn Fields across the State - If you have noticed swollen, blackish-blue, kernels on your corn ears, you are not alone. Over the last few weeks, common smut has been appearing in corn fields across New Mexico. Common smut, caused by the fungus Ustilago maydis, is a common plant disease associated with developing ears of corn. While the appearance of the disease can by quite alarming, the disease usually affects only a few ears and is generally more of a curiosity than a real concern. In fact, in Mexico, after proper preparation, common smut is considered an edible delicacy and not a plant disease. Click here for more information on common smut. Contact: Natalie Goldberg
June 2011
Cucumber Mosaic Virus
Cucumber Mosaic Virus - Are some of your vegetable plants deformed, twisted or elongated? Are the leaves mottled, wrinkled or curled? Are the plants stunted and not producing any fruit? If you answered yes to any of these questions, then your plants may be suffering from Cucumber Mosaic Virus (CMV). This spring we have had a significant number of plants submitted to the NMSU - Plant Diagnostic Clinic (NMSU-PDC) which have tested positive for CMV. This is a common virus, worldwide, and is present every year in New Mexico; but it usually appears later in the growing season and very sporadically. Already this year, we have had a number of greenhouse or hoop-house grown plants infected with the disease. Click here for more information. Contact: Natalie Goldberg
May 2011
Freeze Damaged Plants
Freeze Damaged Plants - To save or not to save, that is the question! The freeze of February 2011 was significant indeed - many areas in New Mexico reported record or near record lows. Las Cruces recorded a low of -5 F and over two days when the temperature did not rise above freezing! Now that spring has arrived, we can start to assess the damage to plants from this event. Perhaps surprisingly, many plants have come out of the winter with no signs of any damage. Unfortunately for others, the story is not so bright. Some plants were killed. Others are struggling to survive. Plants that are still alive, but severely damaged, need to be assessed individually to determine the most appropriate fate. These damaged plants are predisposed to attack by pathogens and insects. In some cases, it may be best to remove these plants than to deal with disease and insect infestation later. If a decision is made to try and save these plants, damaged tissue should be removed in order to eliminate tissue that is attractive to pests. Click here for more on this story. To view videos on how to manage freeze damaged plants featuring the Dona Ana County Extension Agent, click here. Contact: Natalie Goldberg
Curly Top Virus
Curly Top Watch - It's that time of year again, Beet Curly Top Virus may soon be appearing in your gardens. Are your tomato plants curly and not producing fruit? Are your pepper plants stunted and yellow? How about your spinach, squash or beans? Are they deformed, stunted and/or yellow? If you answered yes to any of these questions, your plants might be infected with a disease called Beet Curly Top Virus (BCTV). BCTV is a common disease in many vegetable crops, including tomatoes, peppers, beans, pumpkins, squash, and spinach. It also infects many weeds, which serve as important alternate hosts allowing the virus to survive between growing seasons. The virus is spread from plant to plant by the beet leafhopper. The disease can start appearing in gardens shortly after planting and may continue to infect plants throughout the growing season. Although the lack of significant fall rain would generally indicate that the level of BCTV this year would be relatively low, we have already noticed a significant infection (over 50%) in a spinach planting in the Mesilla Valley. Click on the link above for a publication on this disease. Click here for more photos. Contact: Natalie Goldberg