What is pink eye? 

Pink eye is a disorder of potato tubers that can cause costly storage losses for potato growers and can reduce tuber quality to the point where tubers will be rejected by potato processors.  Pink eye not only directly affects tubers, but also makes tubers more susceptible to diseases such as Pythium leak, bacterial soft rot (see UW Plant Disease Facts D0010, Bacterial Soft Rot), pink rot, and Fusarium dry rot.  These diseases cause additional storage losses and reduction in quality.

What does pink eye look like? 

Pink eye is characterized by a short-lived external pink color that is often, but not always, found around the potato eyes of freshly harvested tubers.  Eyes at the bud ends of tubers (i.e., those farthest from where tubers are attached to stems) more commonly show pink eye symptoms.  Pink eye can eventually develop into corky patch/bull hide, which involves a thickening of areas of tuber skin extending approximately ¹/₁₀ of an inch into the tuber flesh.  Corky patch/bull hide can make tubers unmarketable for either fresh market or processing.

External pink eye symptoms are often accompanied by brown patches in the tuber flesh immediately underneath the skin.  Browning due to pink eye can resemble browning due to other disorders such as internal brown spot or heat necrosis, but these latter disorders tend to occur deeper in the tuber (i.e., inside the vascular ring), rather than just underneath the skin.

Pink eye can also be confused with late blight (see UW Plant Disease Facts D0068, Late Blight).  If there is any question whether the problem might be late blight rather than pink eye, contact your county Extension agent for information on submitting a sample to a diagnostic lab for proper testing.

Where does pink eye come from? 

Pink eye is a physiological disorder (i.e., an abnormality in plant growth), rather than a true disease that involves a disease-causing microorganism.  Pink eye arises during periods of excessive soil moisture and warm temperatures, especially during the later stages of tuber development.  Pink eye symptoms typically appear within seven to 10 days after excessive rain.  Excessive soil moisture coupled with high soil temperature causes a lack of oxygen around potato tubers, leading to damage of cells in the tuber skin.  This cell damage contributes to pink eye development.  Environmental conditions that lead to pink eye also promote tuber infections by the pathogens that cause Pythium leak, bacterial soft rot (see UW Plant Disease Facts D0010, Bacterial Soft Rot), pink rot, and Fusarium dry rot (all diseases associated with pink eye in storage).

How do I salvage potato tubers affected by pink eye? 

Once pink eye symptoms develop, they are permanent.  If symptoms are minor, tubers may still be usable.  However, when pink eye symptoms are severe, symptomatic tubers will be rejected and discarded.

How do I avoid problems with pink eye in the future?  

Growers have no control over the extreme precipitation and high temperatures that promote pink eye development.  However, growers can practice management strategies that minimize water-saturated soils and reduce warm soil temperatures, thus reducing the severity of pink eye.

To minimize water-saturated soils, deep till areas where pink eye has been a problem, areas where water tends to collect for extended periods, and areas where soils may be compacted (e.g., field entrances or head lands).  Deep tillage will break up subsoils in these areas that impede proper drainage during wet weather.  Proper drainage will limit periods when tubers will be oxygen deprived and thus more prone to pink eye development.  Also, avoid any activities that will cause soil compaction such as operation of heavy and large farm tractors and other field equipment when soils are wet.  Minimizing water-saturated soils will not only reduce the likelihood of pink eye development but will also help limit development of other tuber diseases.

To promote cooler soil temperatures, be sure to manage diseases (e.g., potato early dying) that reduce canopy coverage.  Loss of canopy allows soils to warm faster on sunny days, thus leading to higher temperatures that are more favorable for pink eye development.

Finally, be sure to scout for pink eye symptoms prior to and during harvest.  Knowing the severity of pink eye in a field can help growers make informed decisions about the appropriate duration for tuber storage and the best end use for symptomatic tubers.

For more information on pink eye: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

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Growing vegetables from seed is a common practice for many home gardeners.  Unfortunately, vegetable seed (even though it appears perfectly healthy) can sometimes be contaminated with disease-causing organisms, particularly disease-causing bacteria.  Bacterial speck (see UW Plant Disease Facts D0011, Bacterial Speck of Tomato), bacterial spot (see UW Plant Disease Facts D0012, Bacterial Spot of Tomato), and stem canker of tomato, as well as bacterial spot of pepper and black rot of crucifers such as cabbage and broccoli (see UW Plant Disease Facts D0019, Black Rot of Crucifers) are common bacterial diseases where pathogens can be introduced into a garden via contaminated seed.  Making sure your vegetable seed is pathogen free is an important first step in preventing these diseases from being a problem.

Hot-water seed treatment is one method that you can use to eradicate, or at least reduce the level of pathogens (particularly bacterial pathogens), in vegetable seed.  Some commercial vegetable seed companies routinely use this method (as well as other more stringent decontamination methods) to eradicate pathogens.  Hot-water seed treatments are effective because hot water soaks into the seed for a brief time and kills disease-causing organisms, without killing the seed itself.  Other common seed treatments (e.g., fungicide treatments) can also help reduce disease, but typically do not eliminate pathogens that have penetrated the seed coat.

Hot-water seed treatment works best for small seed.  It is not as effective for large or extremely fragile seed, pelleted seed, primed seed (i.e., seed treated to speed germination), fungicide-treated seed, and old seed.  When using hot-water seed treatments, treat only the amount of seed that you plan on planting.  Treatment temperatures and durations will vary depending on the particular crop (see Table 1).

To most effectively hot-water treat seed, use a water bath (in home cooking often referred to as a “water oven”) with precise temperature and timing control.  Such equipment will provide the most consistent and uniform heating, but unfortunately can be somewhat expensive.  Alternatively (but much more of a challenge), you can try to use a large pan heated on a stove.  In order for this method to work, you will need to use a precise thermometer to accurately and frequently measure any changes in temperature.  In addition, you must mix the water thoroughly, adjust the stove settings appropriately and submerge the seed completely during the treatment process to ensure that the seed receive a constant and uniform temperature at all times.  Water that is too hot may injure the seed; water that is too cold will not eradicate pathogens.

To hot-water treat seed, use the following steps:

•  Wrap seed in a permeable cloth (e.g., cheesecloth);
• Thoroughly soak (removing any air) and pre-warm seed in 100°F tap water for ten minutes;
• Transfer seed to tap water heated to the crop-specific prescribed temperature (see Table 1);
• Place seed in cold tap water for five minutes to quickly end the heat treatment;
• Spread seed out on a paper towel or screen to air dry;
• Apply fungicide seed treatments according to the manufacturer’s instructions (optional).

Table 1.  Hot-water treatment temperatures and timings by crop*

*Table modified from http://vegetablemdonline.ppath.cornell.edu/NewsArticles/HotWaterSeedTreatment.html.

For more information on hot-water seed treatment: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

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What is bacterial spot? 

Bacterial spot of tomato is a potentially devastating disease that, in severe cases, can lead to unmarketable fruit and even plant death.  Bacterial spot can occur wherever tomatoes are grown, but is found most frequently in warm, wet climates, as well as in greenhouses.  The disease is often an issue in Wisconsin.

What does bacterial spot look like? 

Bacterial spot can affect all above ground parts of a tomato plant, including the leaves, stems, and fruit.  Bacterial spot appears on leaves as small (less than ⅛ inch), sometimes water-soaked (i.e., wet-looking) circular areas.  Spots may initially be yellow-green but darken to brownish-red as they age.  When the disease is severe, extensive leaf yellowing and leaf loss can also occur.  On green fruit, spots are typically small, raised and blister-like, and may have a yellowish halo.  As fruit mature, the spots enlarge (reaching a maximum size of ¼ inch) and turn brown, scabby and rough.  Mature spots may be raised or sunken with raised edges.  Bacterial spot symptoms can be easily confused with symptoms of another tomato disease called bacterial speck.  For more information on this disease, see UW Plant Disease Facts D0011, Bacterial Speck of Tomato.

Where does bacterial spot come from? 

Bacterial spot of tomato is caused by Xanthomonas vesicatoria, Xanthomonas euvesicatoria, Xanthomonas gardneri, and Xanthomonas perforans.  These bacterial pathogens can be introduced into a garden on contaminated seed and transplants, which may or may not show symptoms.  The pathogens enter plants through natural openings (e.g., stomates), as well as through wounds.  Disease development is favored by warm (75° to 86°F), wet weather.  Wind-driven rain can contribute to more severe disease as the pathogens are splashed and spread to healthy leaves and fruit.  Bacterial spot pathogens can survive well in tomato debris, but they survive very poorly in soil when not associated with debris.

How do I save plants with bacterial spot? 

A plant with bacterial spot cannot be cured.  Remove symptomatic plants from your garden or greenhouse to prevent the spread of bacteria to healthy plants.  Burn (where allowed by local ordinance), bury or hot compost the affected plants, and DO NOT eat symptomatic fruit.  Although bacterial spot pathogens are not human pathogens, the fruit blemishes that they cause can provide entry points for human pathogens that could cause illness.

How can I prevent bacterial spot in the future? 

Plant pathogen-free seed or transplants to prevent the introduction of bacterial spot pathogens on contaminated seed or seedlings.  If a clean seed source is not available or you suspect that your seed is contaminated, consider treating the seed in hot water prior to planting to eliminate the pathogens.  For details on this process, including the proper temperature and length of treatment, see UW Plant Disease Facts D0064, Hot-Water Seed Treatment for Disease Management.  To keep leaves dry and to prevent the spread of the pathogens, avoid overhead watering (e.g., with a wand or sprinkler) of established plants.  Instead use a drip-tape or soaker-hose.  Also, to prevent spread, DO NOT handle plants when they are wet (e.g., from dew), and routinely sterilize tools with either 10% bleach solution or (better due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol).  Where bacterial spot has been a recurring problem, consider using preventative applications of copper-based products registered for use on tomato, especially during warm, wet periods.  Keep in mind however, that if used excessively or for prolonged periods, copper may no longer control the disease.  Be sure to read and follow all label instructions of the product that you select to ensure that you use it in the safest and most effective manner possible.  Burn (where allowed by local ordinance), bury or hot compost tomato debris at the end of the season.  Wait at least one year before planting tomatoes in a given location again, and remove and burn, bury or hot compost any volunteer tomatoes that come up in your garden.

For more information on bacterial spot of tomato: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

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What is bacterial speck? 

Bacterial speck is a common disease of tomato that occurs worldwide wherever tomatoes are grown.  The disease can substantially reduce yield when it severely affects leaves early in the growing season.  The disease can have an even greater impact on quality (and marketability for commercial tomato producers) when symptoms occur on tomato fruit.

What does bacterial speck look like? 

Leaf symptoms of bacterial speck consist of small black spots (approximately ⅛ to ¼ inch in diameter) that often are more prominent on the undersides of leaves.  As the spots age, a yellow halo may develop around the edge.  Spots on fruit are very small (almost pinpoint-like) and do not penetrate very deeply into the tissue.  The spots can be raised, flat or sunken, and range in color from brown to black.  On unripe, green fruits, the spots often have darker green haloes, while on ripe fruits the spots can have subtle, yellow haloes.  Leaf symptoms of bacterial speck can be hard to distinguish from other tomato diseases.  Bacterial spot, (see UW Plant Disease Facts D0012, Bacterial Spot of Tomato) and tomato spotted wilt (a viral disease) may cause similar leaf symptoms.  Laboratory testing may be needed to determine which disease is affecting your tomatoes.

Where does bacterial speck come from? 

Bacterial speck of tomato is caused by the bacterium Pseudomonas syringae pv. tomato.  The bacterium is typically brought into a garden on contaminated tomato seeds or transplants, and thrives in cool (63^°F to 75^°F), wet weather.  It can be moved from plant to plant via splashing water (e.g., from rain or overhead watering with a sprinkler) or on hands and gardening tools when working with contaminated and then healthy plants.  The bacterium can overwinter in dead tomato debris or on porous materials such as wooden plant stakes or trellises.

How do I save tomatoes with bacterial speck? 

Once tomatoes are infected, there is no cure.  You may be tempted to cut off affected leaves as symptoms develop, but this will likely not do much to minimize or slow disease development and may actually promote spread of the pathogen.  Often, the best course of action is to allow the disease to run its course and simply salvage any unblemished fruit as they ripen over the summer.  DO NOT eat symptomatic fruit.  Although the bacterial speck pathogen is not a human pathogen, the fruit blemishes that it causes can provide entry points for human pathogens that could cause illness.

How can I prevent bacterial speck in the future? 

Start by using high quality, pathogen-free seed or transplants from a reputable seed supplier or garden center.  If you have seed that you believe is contaminated with the bacterial speck bacterium and would still like to use it (e.g., it’s a favorite variety with difficult-to-find seed), consider treating the seed in hot water prior to planting to eliminate the pathogen.  For details on this process, including the proper temperature and length of treatment, see UW Plant Disease Facts D0064, Hot-Water Seed Treatment for Disease Management.

To prevent spread of the bacterial speck pathogen from plant to plant in your garden, DO NOT use a sprinkler to water; instead use a soaker or drip hose to water at the bases of plants.  Also, only work with tomato plants when they are dry, and consider routinely disinfecting garden tools with 10% bleach or (better due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol).  Spray disinfectants that contain approximately 70% alcohol can also be used for this purpose.

If you have a problem with bacterial speck, remove contaminated tomato debris from your garden at the end of the growing season.  This material can be deep buried, burned (where allowed by local ordinance) or hot composted.  DO NOT replant tomatoes in the same area the following growing season; instead grow a nonsusceptible vegetable crop.  This approach is referred to as non-host crop rotation.  For more information on this technique, see University of Wisconsin Garden Facts XHT1210, Using Crop Rotation in the Home Vegetable Garden.

As a last resort, consider chemical treatments for bacterial speck control.  If you decide to go this route, use a product that is labeled for use on tomatoes and that contains copper as the active ingredient.  To be most effective, the first treatment must be applied before symptoms have developed.  Apply additional treatments every 10 to 14 days as long as cool, moist conditions continue.  Keep in mind however, that if used excessively or for prolonged periods, copper may no longer control the disease.  Be sure to read and follow all label instructions on the product that you select to ensure that you use it in the safest, most effective manner possible.

For more information on bacterial speck of tomato: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

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What is Verticillium wilt? 

Verticillium wilt is a typically fatal disease that affects a wide range of vegetable crops in Wisconsin.  Vegetables commonly and severely affected by Verticillium wilt include tomato, potato, pepper, eggplant, cucumber, muskmelon, pumpkin and watermelon.  Other vegetables such as asparagus, bean, beet, broccoli, Brussels sprouts, cabbage, cauliflower, celery, chive, collards, garlic, kale, kohlrabi, leek, lettuce, mustard, onion, parsley, peas, radish, rutabaga, spinach and turnip are susceptible to Verticillium wilt, but show less severe symptoms.  Some vegetables, such as sweet corn are immune to the disease.  Many woody and herbaceous ornamentals are also susceptible to Verticillium wilt (see also UW Plant Disease Facts D0121 Verticillium Wilt of Trees and Shrubs).

What does Verticillium wilt look like? 

Initial symptoms of Verticillium wilt include sudden yellowing of foliage, typically first appearing on one side of a plant.  These leaves then wilt and die.  Oftentimes, symptoms mimic the natural aging process of leaves.  Eventually however, the entire plant becomes affected and dies.  By peeling away the outer layers of affected branches or vines, you may observe brown streaking in the vascular (water-conducting) tissue.  Vascular browning is common in tomato and potato plants.

Where does Verticillium wilt come from? 

Verticillium wilt is caused primarily by two fungi, Verticillium dahliae and Verticillium albo-atrum.  These fungi are commonly found in Wisconsin soils.  V. dahliae and V. albo-atrum have wide host ranges including many common weeds, such as ragweed, cocklebur, and velvetleaf.  Susceptible plants and their debris can serve as an overwintering site for these fungi.  In potato, root lesion nematodes (Pratylenchus spp.) can contribute to the development of Verticillium wilt.  However, the role of these nematodes in Verticillium wilt development in other vegetable crops is not well understood.

How do I save a plant with Verticillium wilt? 

Vegetables infected with Verticillium cannot be cured and will eventually die.  However, you can extend the life of infected plants by fertilizing and watering them properly.  Fertilization should be based on a soil nutrient test and should be tailored to the specific vegetables being grown.  Most vegetables require approximately one inch of water per week.  If natural rains are not sufficient, then supplemental water should be applied using a soaker or drip hose.

How do I avoid problems with Verticillium wilt in the future? 

Do not repeatedly grow crops that are highly susceptible to Verticillium wilt in the same area of your garden each year.  Try to rotate highly susceptible crops with other less susceptible crops.  See University of Wisconsin Garden Facts XHT1210, Using Crop Rotation in the Home Vegetable Garden, for details on this process.  Also, try to plant vegetable varieties that are resistant to Verticillium wilt.  In particular, many modern tomato varieties are resistant to the disease.  Watch for varieties with the letter “V” after the variety name.  If Verticillium wilt resistant varieties of your favorite vegetables are not available, select varieties that mature early.  Early maturing varieties are more likely to produce usable vegetables before they eventually succumb to the disease than late maturing varieties.

In addition to using resistant varieties, try to eliminate sources of Verticillium in your garden.  Keep broadleaf weeds under control, as these plants are often susceptible to Verticillium wilt and can serve as a reservoir for the fungus.  DO NOT use mulches that may have been produced from trees (e.g., maple and ash trees) that are susceptible to Verticillium wilt, and immediately collect and discard leaves that have fallen from symptomatic trees.  Also, remove and discard debris from susceptible vegetable plants.  Burn (where allowed by local ordinance) or landfill infected plants and infested plant debris.  DO NOT bury or compost these materials.  Finally, decontaminate any gardening items (e.g., shovels, hoes, plant stakes, pots, working surfaces, etc.) that may have come into contact with Verticillium to prevent spread of the fungus.  Rinse these items with water to remove clinging soil, then treat them for at least 30 seconds with a 10% bleach solution or (preferable for metal tools due its less corrosive properties) 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants).  If you use bleach, be sure to thoroughly rinse and oil metal tools after gardening to prevent rusting.

For more information on Verticillium wilt: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

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What is Septoria leaf spot? 

Septoria leaf spot is one of two common fungal diseases that can devastate tomatoes in both commercial settings and home gardens.  The second common tomato blight, early blight, is detailed in UW Plant Disease Facts D0046, Early Blight.

What does Septoria leaf spot look like? 

Symptoms of Septoria leaf spot first appear at the base of affected plants, where small (approximately ¼ inch diameter) spots appear on leaves and stems.  These spots typically have a whitish center and a dark border.  Eventually multiple spots on a single leaf will merge, leading to extensive destruction of leaf tissue.  Septoria leaf spot can lead to total defoliation of lower leaves and even the death of an infected plant.

Where does Septoria leaf spot come from? 

Septoria leaf spot is caused by the fungus Septoria lycopersici, which survives in plant debris or on infected plants.  Septoria leaf spot symptoms typically begin as plant canopies start to close.  Denser foliage leads to high humidity and longer periods of leaf wetness that favor the disease.

How do I save a plant with Septoria leaf spot? 

Once symptoms of Septoria leaf spot appear, control is difficult.  Thinning of whole plants or removal of selected branches from individual plants may slow the disease by increasing airflow and thus reducing humidity and the length of time that leaves remain wet.  Fungicides labeled for use on vegetables and containing copper or chlorothalonil may also provide control of Septoria leaf spot if they are carefully applied very early in the course of the disease (before symptoms develop is best) and on a regular basis throughout the rest of the growing season.  If you decide to use fungicides for disease control, be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible.

How do I avoid problems with Septoria leaf spot in the future?  

Septoria leaf spot is best controlled using preventative measures.  Destroy infested plants by burning (where allowed by local ordinance) or burying them.  Rotate vegetables to different parts of your garden each year to avoid areas where infested debris (and thus spores of Septoria lycopersici) may be present.  See University of Wisconsin Garden Facts XHT1210, Using Crop Rotation in the Home Vegetable Garden, for details on this technique.  Use Septoria leaf spot-resistant tomato varieties whenever possible.  Increase spacing between plants to increase airflow and decrease humidity and foliage drying time.  Mulch your garden with approximately one inch of a high quality mulch, but DO NOT overmulch as this can lead to wet soils that can contribute to increased humidity.  Finally, where the disease has been a chronic problem, use of preventative applications of a copper or chlorothalonil-containing fungicide labeled for use on vegetables may be warranted.

For more information on Septoria leaf spot: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

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