Saturday, June 26, 2021

Thrips Notes

Some Notes on My Selection Methods

Thrips and Other Spring Problems

I wanted to discuss my process of selection for thrips resistance a bit in this post. In a recent private message someone asked me, “If you’ve done all this rouging for thrip problems, why are you still having trouble with them?” I’m not sure what spirit this was asked in, but I took it as a legitimate and interesting question, and one I was happy to answer. It was also thought-provoking for me, and gave me a chance to explain my process. I am not naming the correspondent in this post, because I am not here to call anyone out, and I honestly appreciate the question. Here is my reply.

“Thanks for this interesting question. It is true that I have been selecting for thrips resistance, along with resistance to drought and late freezes in my early program for several years now. There are multiple reasons that I still see thrips in a bad year.

"The first and most important is that I don’t spray my gardens for them. I do spray the plants I send out to people, and I clean them meticulously to ensure that I don’t inadvertently spread thrips (though they are already endemic to most of the US), but in my own growing setup I don’t spray at all so that I can have the full assault of thrips in the early season when there are stressors like drought and late freezes. Thrips in my region are most intense during April and May, and sometimes into June, though in consistently wet conditions, they cause far less damage and are less active. Very dry conditions is their favorite time to swarm out of the ground and feed, it seems. I purposely don’t spray to keep selection pressure high. It has been my experience through years of observation that most daylilies have poor thrips resistance. This is most obvious in darker anthocyanic colors such as red or burgundy, but none of the colors are immune, and some non-anthocyanic colors are just as susceptible as any red or purple. It is also my experience that very few daylilies show high thrip resistance. People tell me that most of their daylilies are fairly resistant to thrips, aphids and other damaging insects, but I suspect they have never seen what these pests can do in the right setting. My conditions are a dry hillside with little topsoil, and even though there is a lot of clay, it still dries out quickly, being mixed with sand. When there is considerable rainfall, my soil holds water well, but due to the sand it dries out quickly, and once dry, stays that way until heavily saturated again. This gives me a special situation where I can make breeding advancements in resistance to these and similar difficult situations and pests, as for several decades I have noted some daylilies that do great when the majority are hit with the right conditions to produce heavy stress in the plants and a heavy thrips infestation.

A daylily flower showing spotting and deformity. Such problems do not have only one cause, and while thrips can cause such unsightly problems, so can other insects, such as aphids. Further, thrips alone may not be able to cause these issues (or at least not to this extent). I note the worst problems for deformed and spotted flowers occur to the early/early and early flowering types, and the issues are worst in years when there is a confluence of multiple stressors while the scapes are forming - i.e, in my gardens, a year combining multiple severe late spring freezes, some level of drought as the scapes are emerging, and the inevitable thrips explosion that coincides with dry conditions in my spring garden.

"Next, because few daylilies show high resistance to thrips and other conditions such as drought and late freezes, and especially so amongst early-early and early types that happen to be forming their scapes earlier than later flowering types, selecting proper breeding materials has been like finding a needle in a haystack. I spent several years just making crosses of those few I could find and observing how the inheritance turned out in order to formulate a plan of action. I don’t yet have a “thrips resistance program”. What I have are a handful of individual plants that have been recurrently resistant to the stressors of early spring in my area, and which, for whatever reason, are not as effected by thrips as others, as well as their most resistant offspring through the first and second generations. That is not a line. That is raw materials. What I have shown to my own satisfaction is that thrips resistance is heritable and replicable within a breeding program. 

"However, another factor to consider is that I have not just been breeding for these traits, and have been selecting for other esoteric traits such as rust resistance and a plethora of plant and obvious, exoteric flower traits. Because so few daylilies show the extreme late freeze/drought/thrips/aphids resistance that I desire, there are other important (to me) traits that might be lost if I solely used those with the above listed observed resistance. This then requires compromise, and especially among the plants that went through multiple years of rust resistance selection. To ensure I had a good number off rust resistant individuals representing multiple different founder plants, I have been slow to cull the best for rust resistance for thrips susceptibility too quickly or feverishly. My process has been slow in this regard as I am loath to cull those that showed rust resistance too precipitously. So, for instance, the first seedlings I made in 2011 and 2012 went through all five years of my rust resistance selection. Now, 9 to 10 years after those were bred, I have gradually culled away almost all the thrips problems from these plants, and am focused on a handful of plants showing moderately high to very high thrips resistance, plus many other good traits. Plants that went through the rust culling of later years, 2013 - 2016 (when the screening period ended) have been given more leeway. Because of that, in good years, when the conditions have not been right to reveal all the shortcomings, I have frequently kept plants that I might then end up culling later. We all do this. It is hard to let go of something you like, for whatever reason (and I am kind of a die-hard, anyhow). That means every time there is a really intense year for conditions to induce heavy thrips activity, a bunch of things get revealed to be inferior in that regard and get eliminated. I don’t get these bad years every year, and there may be two or three (or more) good years between the worst ones.

Me evaluating daylilies in the early season garden. Here, I am inspecting my 2019 introduction 'The Spice Must Flow', which shows excellent resistance to the manifold early season issues I frequently see. Solaris Symmetry, ever reliable in the early season in my garden, foreground, and directly behind Solaris Symmetry is a seedling that is Solaris Symmetry x Implausibility, and is a half-sibling to 'The Spice Must Flow' through Implausibility. It also shows extremely good resistance to the early season issues and has since it first flowered in 2014.

"Another layer is “point of reference” or “point of comparison”. In short, what might look good when there are much worse things around to be culled, may look far worse without those bad things present to be compared too. If a plant's flowers are in the middle of the group when the worst are present, once the worst are gone, that moderate flower may become the worst in the group, and in this way, problem plants are gradually eliminated until the remaining represent perhaps the top ten percent or less of the original population. All programs do this within the parameters for which they are selecting, because you just can’t grow them all, and if you have too much, the truly exceptional can get lost in a sea of data and overload. In 2020 I had a quite good year and everything was fairly beautiful, and while there was a little flash of thrips right at the beginning of the season, they didn’t last long or cause tremendous damage. That year I made my final flower culling on a huge number of seedlings that went through the last four years of my rust resistance selection phase (2013 - 2016), leaving me with about 300 seedlings from those years. This year is giving me the opportunity to observe some of these for the first time in a difficult year, and so I am making further inroads into this group. It is a blessing on many levels. For instance, I have been tepidly beginning to experiment with breeding from some of these for a few years now, but have not made final selections to move anything into my base plant category at the secondary level, so this type of elimination is really important to get any of these into that level (and there will be a few that make that level from those hybridizing years). Because all the seedlings left from 2013 - 2016 had shown significant rust resistance, I have been quite slow and forgiving in terms of culling for certain problems (and more so with the tets than with dip seedlings, as tets show fewer resistant cultivars, and so I have felt a sense of urgency to maintain as many originator lines as possible for this trait). This year though is bad enough that a bunch of these have to go. Last year I eliminated thousands, because I finally had the kind of year, and was in the place where I could, cull all those resistant seedlings down to the most impressive flowers from their respective crosses. This is the kind of year when I can now take that down further by eliminating those that just don’t hold up to early spring stressors. 

"Another hitch is that I ended up with far more early-early and early season plants than I would like. This part of the season has rarely done well in my environment. I have never been a big fan of this part of the season in my garden, but by chance, some of my most important base plants (Ancient Elf, Solaris Symmetry, Implausibility) turned out to be early-early to early flowering in my garden, and because they got used heavily, much of my program skewed that direction. It wasn’t really intentional, but since Solaris Symmetry is one of the most freeze tolerant/drought tolerant/pest tolerant of the early types, and fancy modern types in general, it has turned out that I have been able to make some significant strides in this area - i.e., I have more than enough seedlings with Solaris Symmetry in the ancestry that also show the very high tolerance to these problems to make a real breeding program. It's there, so I might as well exploit it. Another thing I have done is to watch amongst the seedlings of these early-early and early types for later blooming seedlings, as my favorite season is the late and very late, and I am always keen to bring those excellent early genetics into that season. So there are lots of threads in my breeding program, and they are all gradually being woven into what I consider to be the ideal garden daylily with superior plant traits and gorgeous, modern flowers that hold up under adverse conditions on big, bold, fertile, healthy plants. That is a lifetime’s work, though.

My 2021 introduction 'Elizabethan Rainbow Portrait' regularly shows excellent performance in good years and bad and has extremely good breeding ability for passing on that resilience.

"Finally, one other thing to consider is that I don’t automatically compost every cultivar that shows some thrips issues. We have early-flowering cultivars here from a wider range of programs that show mild to heavy thrip susceptibility in a bad year, but that look good enough in a good year and for whatever reasons we continue to grow them in our flower beds. Someday I may only grow my own most resistant selections, but that isn’t something we want to do now. Some of the old cultivars just have sentimental value, after all, and some have one or another very desirable traits while also having some undesirable traits. I don’t tend to write much about the problems of these cultivars, because my point is not to call out other programs, but to simply work toward improvement, if for no other reason than my own driven nature and satisfaction. Each year sees a further refinement of what I am working with, the seedlings I am keeping and the individual plants I am using in hybridizing. Here in my tenth full year of hybridizing, I can say I have the materials to now start my program and build toward the type of daylily cultivars I envision. Here’s to the next decade (because this kind of work is slow by its nature)!"