Plant Diseases - Nematodes

This time I’m researching nematodes, which are non-segmented round worms found in soil, water, and extreme environments such as deserts and ice fields. A few can be seen with the naked eye, but most are tiny and require magnification. For resources I’m using Essential Plant Pathology, information from my plant diseases course at Merritt College in Fall 2012, and Five Kingdoms. Keep in mind that most nematodes are beneficial – they aerate the soil, consume detritus, feed on bacteria and other small life forms, and circulate organic and mineral soil components. Others cause considerable damage to crops, turf, and plants in the landscape. Nematodes can be found in the San Francisco Bay Area.

Nematodes are categorized as Eukarya in the Animalia kingdom. About 10% of all nematodes are plant parasites, and require a living host (obligate parasites). They are aquatic and typically live, feed, and move in the soil. They use a specialized feeding structure—called a stylet—to penetrate plant tissue, probe, secrete proteins and polysaccharides, and ingest cellular contents. Most nematodes are migratory and move from cell to cell to feed (ectoparasites). Others are sedentary and remain embedded in a plant throughout their lifecycles (endoparasites); some endoparasites induce formation of specialized feeding sites, such as galls, where they live and feed. A few do not fit either of these categories.

The female nematode lays hundreds of hardy eggs (some species do not require male fertilization of the eggs). The eggs can exist in soil for years or decades, until the right environmental conditions exist for them to infect a plant. Their life cycle includes four juvenile stages. Nematodes molt, shedding the outside cuticle and part of the lining of the stylet, from stage to stage as they grow. Juveniles look like miniature adults through all stages (they do not undergo a metamorphosis from stage to stage).

Take a look at several nematodes; of special interest (1) views of the stylet at 57, 107, and 145 seconds, (2) a root rot nematode at 159 seconds, and (3) a needle nematode at 202 seconds: http://youtu.be/Qf8oGjqyXFc

On the Roof at MOMA

I am always on the lookout for roof top gardens. They can be elaborate and extensive, or a quiet and private space. On one of our son’s visits home from University of Alaska, Anchorage, we visited the San Francisco Museum of Modern Art (or MOMA) to view their art collection. The building was designed by Jensen Architects (an international firm based in San Francisco), and is very distinctive.

One of the fun discoveries was the Carolyn and Preston Butcher Garden Terrace, with its roof top sculpture garden and small coffee bar. We spent part of our MOMA visit on the roof, enjoying the combination of closed and open air space, and interesting sculptures. I also enjoyed the chance to study the raised planting areas and choice of vegetation. It was simple, yet very satisfying.

Carolyn and Preston Butcher Garden Terrace (MOMA) - raised bed

The museum closed earlier this summer for a three-year renovation project. See their web site for information about their off-site exhibition this fall (http://www.sfmoma.org/). You can catch a glimpse of the Garden Terrace in the short video “Trailer for Stories from the Evacuation” (fast forward to 1:11).

Clear Lake Plant Diseases

I’m afraid my Plant Diseases class from Merritt College in Oakland has despoiled me – I am always on the lookout for plant diseases! End-of-summer is a great time to spot them, as many plants have spent their reserves on reproduction, and are more vulnerable to attack. Here are some of the diseases I spotted in Clear Lake; oaks seem especially hard hit.



Sudden Oak Death –  I wasn't close enough for direct inspection, but this looks like SOD from afar; caused by the water mold, Phytophthora ramorum. 

Oak Gall – these little "nipples" are galls caused by asexual reproduction by the oak gall wasp.
When the wasp lays its eggs, hormones kick off a type of genetic engineering to create the perfect nursery (the gall).

Oak Apple Gall – this "strange fruit" indicates sexual reproduction by the oak gall wasp.

Tent Caterpillar – we found these gauzy structures all over foliage.
The residents had already moved on.

In many cases, these diseases do not cause permanent damage. An organism is simply taking advantage of a situation, and working through its own life cycle. After the class, seeing plant disease is not necessarily alarming. Plants in nature are rarely perfect; instead, they are teaming with all sorts of life forms. Learning to enjoy the whole ecosystem of a plant, both good and bad, can add to the enjoyment of nature as well as the garden. And raising your tolerance for imperfection can lower the need to combat the imperfect with pesticides.