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After some cursory experimentation, I found a few ways of treating minor cases of leaf spot on rhododendron foliage. I also found a way of making prognoses and deciding whether or not to remove a leaf-spot afflicted leaf.
1. How to tell if it is better to remove a leaf or if it is better to treat relative to the well being of the entire plant:
A) Is the leaf more than two thirds covered with lesions? If so, remove it.
B) Is the leaf near the bottom of the plant? If so, proceed to step B2. If not, proceed to step C.
B2) Is the plant mature and well branched? If so, remove the leaf.
C) Is the leaf directly above and/or adjacent to other leaves? If so, remove it.
2. How to treat minor cases of leaf spot:
If the lesion is near the tip of the leaf, make a horizontal section of the leaf just below it.
If the lesion is contained by the venation of the leaf, keep the leaf dry during the day.
I am working on producing a detailed description of the lesions, including coloration, spread timing, effects on productivity, positional growth with respect to veins and margins, etc.
So far, I've distinguished two kinds of leaf spot by lesion coloration and associated symptoms.
Type I:
Tan center, brown middle layer, purple perimeter. Eventually decays, forming holes where the lesions were. Causes chlorosis (firing) in certain parts of the leaf. If it occurs on a vein, all the areas supplied by that vein between the lesion and the leaf's tip will display chlorosis.
Type II:
Brown center, wide black perimeter. Does not decay into holes. Does not cause chlorosis, but will spread rapidly with heat and water. Lesion can cover a whole leaf in bad cases. Spreads in water especially at midday.
Part I:
Leaf miners are generally noticed affecting the leaves of the host, showing long lesions of a width of slightly more than one centimeter. These lesions may be colored brown, tan, or white. The cause of disease is a species of moth or butterfly specific to the host species. Two specific variations have so far been observed:
Variation One: Host species is Plantago major, commonly known as broadleaf plantain. The lesions are a tan-brown and black spots about a milimeter thick by around five milimeters long can be seen at the center of the lesions. These lesions generally start somewhere in the perimeter of the leaf and eventually converge with the midvein after some length. The cause is a brownish nocturnal moth, which can be seen at lights during the night, with an approximately 1" wing span and red eyes. (See thread "Pesty Nocturnal Moth" in 'Insects' forum for photo).
Variation Two: Host species is Viola papilionacea, commonly known as wild violet. The lesions are white and tiny caterpillars about one millimeter in width and five or more millimeters in length can be seen with the naked eye. If cut in two, a green hemolymph fluid will ooze out of the sectioned caterpillar's viscera. The lesions generally originate towards the leaf's perimeter, especially below the third pair of veins. The cause is a moth about 3/4" in wingspan with black eyes and clubbed antennae that can be observed at lights during the night. (See my photo album titled "Case Histories of Afflictions of Forbs and Grasses" for photo).
Part II:
Poplars often develop a foliage affliction that is manifest as a whitening of the perimeters (especially below the third vein pair) of the leaflet. The whitening occurs in a mottled pattern, and is quite contagious via leaf and sap contact. Most curiously, this affliction never appears manifestly on the seed leaves. The already-developed discoloration will appear dulled after a direct application of the garlic mustard root extract to the affected areas; nevertheless, the affliction will continue to spread.
My first botanical written work, Aegrae Ex Morbis Herbae Graminumque (transl. "Cases Of The Diseases Of Forbs And Grasses" in Latin--my language of choice for writing with great care and detail). I have started investigating three cases, one of which ended in the specimen experiencing what I termed "mors lepore" (transl. "death by rabbit"). Between the three cases, I am closely investigating two afflictions (or what appear to be afflictions, at least).
The first case has presented a stern difficulty due to a lack of background knowledge on my part. The specific host plant that I have observed in my cases numbered I and III is the only plant that ever shows the symptoms, and the specific symptoms show on every plant of this particular species, thus I am faced with a dilemma as to whether or not the symptom is natural or unnatural. The symptoms are mosaic-like yellowing of the leaves and abnormal distribution/progression of growth causing the leaf to bend. I have extensive photo-documentation, yet I cannot solve this problem. Some pictures of my first case are in an album of mine on this site titled "Cases Of The Diseases Of Forbs And Grasses" if anyone would like to see said symptoms. In short: I will get nowhere with this case until I can verify the abnormality of the symptoms by identifying the host plant.
I have had much more success with the second case and the related affliction, despite the abrupt disappearance of my specimen due to the frustrating incidence of "mors lepore." My specimen now lies in the intestines of said glutton. The symptoms and disease were so apparent that I could identify the affliction on the spot--leaf miners. The host was broadleaf plantain ([i]Plantago major[/i]), and the spread of the disease was specific to that species of plant. In addition to my written case history, I had precise documentation of the outbreak of symptoms across the defined regions of my yard and of the daily progression. To top it all off, I managed to identify and take a picture of the moth whose larvae cause the disease in Plantago major. Soon I will finish writing the case history and description of the affliction, then I can focus more on the first and third cases described before.
Now, as practical advice to those readers who are struggling with diseases in their lawns or gardens, I have another observation to relate here. I noticed that large trees, including oaks and maples, will drop their leaves deliberately (abscission) when the leaflets or entire leaf is diseased. If these leaves fall and are let into your lawn or garden, they could spread such afflictions as leaf spot, spider mites, aphids, scale, whiteflies, and nearly any pest or fungal affliction to your plants. Thus, my advice is: keep leaves that fall in spring or summer away from your garden!
P.S. If anyone has any difficulty in their garden or lawn with weeds, insect/arachnid or fungal pests, or disease, I would be more than happy to help, if I can in any way.
Well, after neglecting my indoor garden and my hobby for some time now, I've come back. Fortunately, I have been taking mental note of changes in the outdoor flora, but I nevertheless have limited data, especially when it comes to dating germination, blooming, and disappearance of certain plant kinds. I have written nothing in my notebook till now, and am constrained for time. Hopefully, I will be able to document the characteristics of the major plant kinds that have appeared (some kind of violet, garlic mustard, ragweed, bracken ferns, dandelions, white clover, broadleaf plantain, mock strawberry, English ivy, creeping woodsorrel, maple seedlings, and many unknowns) and disappeared (bittercress, purple deadnettle, and one or two unknowns) lately.
Unfortunately, my expansive indoor garden completely died out as a result of my neglect. I shall have to start again from scratch, and I will have to keep it limited to a few simpler specimens.
If anyone has some seasonal observations for this year's weeds, I'd love to hear them.
Although I do have so many plans for writings and experiments, I have not written down many observations or explanations for observations this week. It was somewhat slow this week, but I did make a few key revisions and observations.
Firstly, I did much revising of inaccurate identifications. Early in the week, I realized that I have a variety of species of speedwells and perhaps a variety of deadnettle species as well. I believe that I have three species of speedwell, but I can only identify one with near-absolute certainty. The certain species is ivy leaf speedwell, and I suspect that the other two are corn speedwell and Persian speedwell, but, again, I am uncertain. I have not seen the unique mature leaves of corn speedwell, but the speedwells I have seen are very small, except for those I harbor indoors. I am now certain that the plant I formerly assumed was henbit is actually one of the closely related and similar deadnettles. It is possible that there are several species of deadnettle present.
Then, I brought a new seedling of common speedwell indoors. My last attempt at keeping this plant was unsuccessful, because it did not tolerate the excessive sunlight. I moved my surviving mouse-ear chickweed seedlings as well as my new common chickweed seedling to a more easterly window. I also have a second wood sorrel seedling that grew with my deadnettle. Wood sorrel is not a wide-spread species in my back yard, and I have only observed three or four members of the population. It does seem that its seeds cover a large area oddly enough, but only germinate at higher soil temperatures.
In these last few days, I made more progress than in any week of February. I made three new identifications that I am quite sure of, recorded the flowering of four plants, wrote three new species accounts, began writing on two new topics in my notebook, revised my writing on dynamic plant growth (I posted the revised page in an album), began studying six new phenomena, and obtained a specimen of a previously uncollected species, wood sorrel.
My garden inventory: 4 mouse-ear chickweed, 1 henbit, 3 corn speedwell, 2 ivy-leaf speedwell, 3 unknown tiny rosettes, 1 wood sorrel, 1 dandelion, 1 horseweed, 6 hairy bittercresses, and 3 common chickweed.
New identifications: ivy-leaf speedwell, corn speedwell, henbit
New samples: wood sorrel
New topics to be written (excluding species accounts): Node development in oak twigs and in general, flowering, germination and seed structure, moss anatomy and the tempo of moss life cycles, the speedwells and their morphological distinctions, the growth of axillary and terminal buds, and in-depth leaf structure.
Completed Topics: Species accounts of both ivy-leaf and corn speedwell and a revision of my theory of dynamic plant growth.
Topics still being written: Astronomical references for the developmental stages of hairy bittercress and a lunar calendar of botanical events in late winter and early spring (Jan.->March).
Planned experiments: Cross pollination of corn and ivy-leaf speedwells--I hypothesize that there is a reproductive barrier pertaining to hybrid breakdown or hybrid sterility. Another likely possibility is that there is a reproductive barrier as either a mechanical or gametic barrier. I will write a detailed report of the experiment, per the current laboratory report conventions, and will only accept my hypothesis if my results are within the conventional range of probable accuracy using the chi-square distribution.
Bad weather has kept me indoors for most of the month, but I have made some interesting observations on the plants I collected earlier. For one, I was able to properly identify the plant I had quite erratically thought to be broadleaf plantain as a juvenile horseweed, with the help of told2b on the plant identification forums. I noticed that the seedlings I had suspected to be garlic mustard were in fact not, as I saw that they had begun to form what appear to be palmate lobes. I will have to wait to see what these seedlings are. Also, with the help of a nutrient deficiency in one of my containers, I was able to explain why henbit was more resistant to spider mites than common chickweed in my early experiments. I have properly identified the grassy weed I once thought to be crows-foot as a kind of crabgrass. I recorded observations of the mature growth of hairy bittercress, and will need to rewrite the page in my notebook concerning this. I have observed firing, a discoloration of leaves from nitrogen deficiency, in some of my container-grown henbit, chickweed, bittercresses, and corn speedwell as mentioned earlier. I tasted some leaves of bittercress, only to find them not so bitter as others have said. It is very mild in taste, and tinged slightly with bitterness. The taste of the mature and juvenile leaves is no different. Most intriguing, I found that what I had thought to be a lichen growing on oak trees in the backyard are actually liverworts. Lastly, I found three seedlings of a previously observed unknown species, which I suspect may be horseweed.
Indoor garden: I have started using a new container design, tomato jars with a punctured zip-lock bag sealed over the mouth with the plant inside. It appears to work quite well. I made a few additions: three mouse-ear chickweed seedlings, four unknown (horseweed?) seedlings, a small patch of peat moss, two juvenile bittercresses, two somewhat odd-looking bittercresses of a very small size from the other side of the yard, one unknown seedling (perhaps an amaranth of some sort), and two small crabgrasses. I have just about run out of space on the windowsill.
New observations and concepts: I did some follow-up on general plant production and growth from my observations in my spider mite experiment recently by observing leaf discoloration in a soil lacking in nutrients. I inducted that henbit does not concentrate as much of its development into vertical growth as common chickweed does, giving it a better chance of surviving pest infestations as I observed in the former experiment. I also inducted that bittercress complex leaves undergo a development similar to the erect stem of common chickweed, where the larger terminal leaflet provides for the development of the lesser leaflets until they are able to provide for themselves. This would explain much about rosette growth, but I yet cannot perceive how the nodes form in a rosette, nor how the pinnate leaflets develop in spite of their proximity to the sub-nodes of the complex leaf. I observed a curious difference in the stem color of erect and creeping corn speedwell. Lastly, I observed the patterns of winds and exposure to them throughout the yard.
Pending topics: Soil capacity for growth (quantifying the factors of soil fertility), stem color changes (chickweed and corn speedwell), dissection of compound leaves in their development (pre-dissected or dissected as they develop), daily and long-term timings of mosses and liverworts, lunar cycles and plant development, nodes and their spacing, and grass anatomy.
I haven't found any new species, but I've spent some time considering what I've observed over the last few months. Meanwhile, I am also making recorded observations of the various plants I've seen in the last few months, and their tendencies. Among other things, I described the growth patterns of some winter annuals. I scanned a page of my journal that describes the growth of winter annual and biennial garlic mustard and put uploaded the image to the "Garlic mustard" photo album. I wrote a description like this for hairy bittercress too.
My indoor garden: I've been growing a few small plants in some glass and plastic jars sitting a windowsill in my workroom. I keep that window's curtain closed at night so that the ceiling lights do not disturb the plants' circadian rhythm. I also open the jars several times a day to refresh the CO2 supply, but I think the plants (especially those in smaller containers or sharing the CO2 supply with other plants) have started losing organic molecules because of photorespiration. Nonetheless, none of the plants would have the slightest chance of survival in the dryness air in the room. Here's an inventory of what I have growing there: three common chickweeds, six henbits, three hairy bittercresses, two mouse-ear chickweeds, two corn speedwells, and four plants that I'm not sure of. Three of these uncertain plants are seedlings that I am nearly certain will become garlic mustard; nevertheless, I will wait to confirm until the plant has matured enough that I can better identify it. The last plant is much like a developing broadleaf plantain, but has a couple of pairs of notches along the leaf margins, petioles that measure a greater length from the end of the leaf margin to the the basal center than the measure of the length of the leaf. I will soon ask about this plant on the identification forum.
My collection inventory: I don't have any stores of dried leaves, stems, or roots of high enough quality for any use other than being a part of my collection of dried plants. The volume of those dried plants has become too much for any small container, so I plan to keep imprints in a notebook instead of dried leaves in a small plastic box.
My current gardening tasks: I have been recording the growth of wild seedlings for the past few weeks, as well as identifying the last bunch of winter plants. Additionally, I have been trying to imagine what I might do for a formal garden next year. I was especially considering what plants to grow. Bittercress, plantain, henbit, and wild onion are some available candidates, but I am tempted to get some seeds too. Initially, I wanted to limit what I grew to what I wanted to study from my backyard, but the limited selection of available plants can be frustrating. In particular, there are no plants here that I know of with strong fibers for making twine.
[January]
Now I've found many, many
different kinds of plants, and learned much about how they thrive. It
seems to me like there could be no more gratifying use of time than
exploring the backyard, even if I don't live in the most exciting
zone. I have observed plant growth, function, advantages, and
tendencies for a few months now, in addition to studying externally,
and I seem to have more questions than when I began studying plant
life, and so I am very thankful to have the community on
GardenGuides.com for help.
So far, I have collected (and identified) the following (vascular) plants:
Common Chickweed (Stellaria media), Mouse-ear Chickweed (Cerastium vulgaris), Periwinkle (vinca minor), Hairy Bittercress (Cardamine Hirusta), Creeping Wood Sorrel (Oxalis corniculata), White clover (Trifolium repens), American Holly (Ilex opaca), Indian strawberry (Duchesnea indica), Garlic mustard (Alliaria petiolata), Common Pricklyash (Zanthoxylum americanum), Greenbriar (Smilax rotundifolia), English ivy (Hedera helix), Broadleaf Plantain (Plantago maior), and Prostrate knotweed (Polygonum aviculare). For vascular leafless plants I identified: Wild Onion (Allium canadense), Crabgrass (Digitaria sanguinalis), and Goosegrass (Galium aparine). I've only found one non-vascular plant so far: peat moss.
I am growing several species of weeds indoors. The point is not to grow weeds for the sake of growing weeds, but to study these plants. I keep detailed records of what I observe, comparative experiments I devise to learn more about the plants, diseases, growth patterns, etc. Currently my 'garden' is a collection of glass containers filled with water and each with some plant or another growing inside. I have growing eleven different chickweed plants, twelve winter bittercress plants, a great plantain, a prostrate knotweed, and three unknowns.
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