Field Crop News

Website Address: http://fcn.agronomy.psu.edu/

April 18, 2006    Vol. 06:02

IN THIS ISSUE:

Mark Your Calendar

Weather Outlook

Production

Pest Management

WEATHER OUTLOOK

The dry winter is yielding to a dry first half of the spring. In addition to the drought watch issued in early April, the state will soon be near its peak risk for brush fires. The weather pattern shows a temporary break in the very mild, dry conditions for the period April 22–25. A sluggish disturbance from the Midwest will initiate showers on Saturday and the opportunity for showers will continue into Monday and perhaps Tuesday. While nighttime readings will be milder in the moist air, daytime temperatures will struggle to reach seasonal levels — especially in the eastern half of the state where onshore winds will push maritime air inland. It will likely take a push of Canadian air to bring back sunshine and dry weather again by the middle of next week which should persist into the weekend. The overall pattern favors streaks of dull, cool and damp conditions interspersed with spells of very warm and dry weather through May. In the mean, temperatures will average above normal and precipitation will stay below normal, though not as dry as late March and April have been. An analysis of dry and wet spells in Pennsylvania indicates that once a regime has been established, the most probable length is 26–28 months. If we mark the current dry spell as beginning last May (2005), then most months through autumn 2007 will average drier than normal. Of course, even in this dry pattern, October 2005 brought record rainfall to parts of the state.

Paul Knight, pgk2@psu.edu
Pennsylvania State Climatologist

PRODUCTION

SCOUTING EMERGENCE PROBLEMS IN CORN

Corn planting is advancing rapidly this spring and soon we will be evaluating our corn stands. Timely scouting for corn emergence problems is an essential part of a top corn management program. Early diagnosis of problem fields can lead to timely replanting decisions and management changes that can avoid future problems. Corn should begin emerging after about 100 to 150 GDDs have accumulated following planting, so plan scouting accordingly. Here’s a list of a few common problems encountered during this phase:

Figure 1. Uneven emergence due to shallow planting in tilled seedbeds.
  1. No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.
  2. Coleoptile unfurled underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, or may be due to extended cool wet conditions alone.
  3. Seed with poorly developed radicle or coleptile. Coleoptile tip brown or yellow. Could be seed rots or seed with low vigor.
  4. Seed swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. This could be a particular problem this year in tilled seedbeds if corn is planted less than 1.5 inches. Check seed furrow closure in no-till. Seed may also not be viable.
  5. Skips associated with discolored and malformed seedlings. May be herbicide or insect damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants. Look for wireworm or garden symphalins feeding on roots or seeds.
  6. Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.

Note the patterns of poor emergence. At times they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing. This information is valuable to assess planter performance.

Greg Roth, gwr@psu.edu
Corn, Soybean, and Small Grain Management, Crop and Soil Sciences

DROUGHT MANAGEMENT

Because of March’s lack of rainfall, the state Department of Environmental Protection declared a drought watch that asks state residents to cut back on nonessential water-use by 5 percent. March and April are generally the last months that offer opportunities to recharge the soil profile and groundwater, but have been very dry this year. This has implications for summer crop production.

Precipitation can go 6 ways after it falls: infiltrate, run off, evaporate, transpire, percolate to groundwater, or be stored in the soil. Farmers want to do whatever they can to maximize infiltration and soil water storage and reduce runoff and evaporation. Because farmers need to produce, it makes most sense to maximize transpiration of the economic crop — the water that the crop takes up and is then lost from the crop leaves. Substantial percolation will happen only after the soil profile has been totally saturated — something that’s not likely in the near term.

In the middle of summer, it is not uncommon for a crop like corn or alfalfa to transpire 0.3″ per day — 9 inches per month. However, average monthly precipitation across most of Pennsylvania is only about 4 inches. This means we rely on soil water storage to carry us through the summer. This is where soil differences show up — a deep soil with few rock fragments can store a lot more water than a shallow or rocky soil. Whatever the case, with the low soil water reserves, it becomes important to recharge the soil profile for the summer crop, not deplete it. So what can a farmer do now to increase soil water storage?

One of the big management decisions farmers face at this moment is to terminate cover crops of rye or to wait and harvest them for forage. Rye takes up a lot of moisture from this point forward. However, if we dessicate it with a herbicide and leave the dead rye at the surface, the mulch will actually save water! With ryelage yields being a lot lower than corn yields, and rye often being a lower quality forage, it starts to make sense to burn the rye down now to guarantee more soil water for the summer crop. Short-term fodder needs play a role also, of course, and may lead a farmer to decide to harvest the rye for ryelage anyways.

Figure 2. No-till saves moisture.

Another decision farmers have now is to use no-till or tillage. Tillage leads to more soil water evaporation. First, exposing moist soil to the atmosphere helps to dry the soil out, and after that the bare soil loses more moisture to evaporation. The bare soil also tends to produce more runoff. In contrast, the no-till soil is covered with mulch, which helps to reduce evaporation and increase infiltration. Of course, there are intermediate choices — plowing with a moldboard plow dries soil out most, whereas chisel plowing dries the soil out less. Leaving the field in a rough condition after primary tillage also stimulates more moisture loss because of a larger exposed surface, so it’s important to get that secondary tillage done as soon as possible. Secondary tillage implements also become important — using a field cultivator brings mulch to the surface, whereas a disk harrow tends to bury it. More mulch means less evaporation and more infiltration.

Other choices farmers have include timely burndown of weeds and cover crops and good weed control in the summer. Remember that weeds rob water from the crop. Optimal pH and soil fertility allow crops to make maximum use of water. One might also think about reducing plant populations — high plant populations usually pay only when plenty of moisture is available. On shallow, rocky soils high plant populations are less likely to pay this summer than on deep soils.

Sjoerd Duiker, swd10@psu.edu
Soil Management, Crop and Soil Sciences

BEWARE OF PLANTER PENETRATION

With dry soil conditions it may be very challenging to get adequate planter and drill penetration, especially in short-term no-till. Why is this? A major reason is the loss of water that normally surrounds cations that bridge negatively charged clay particles. The non-hydrated cations create a very strong bonding (like cement), unlike hydrated cations. In other words: the soil becomes like concrete. Another bonding agent is humus (highly decomposed organic matter). The humus-clay bonds are not as strong, even when the soil is dry, which is the reason high organic matter content helps maintain good soil tilth whatever the soil moisture conditions. High humus content builds up at the surface of long-term no-till soils, and can also be increased by adding manure, sewage sludge and compost to soil.

With dry soil conditions, the most challenging situations are planting corn after a spring cutting of hay was taken off, or after ryelage harvest. Other challenging conditions are to plant into soybean stubble late in the spring, when the soil tends to become as hard as a rock. Compacted corn silage ground is another one to watch out for. On the other hand, planting into a timely killed cover crop or corn residue where there is good mulch cover tends to be easier because the mulch saves moisture, and the roots of the cover crops help improve soil structure.

In dry, hard soil conditions, it is very important to pay attention to planter penetration and seed depth placement. Every piece of iron that you have to press into the soil now becomes a liability. So using pop-up instead of 2×2 injected starter fertilizer is advantageous. It may also be possible to take coulters off the planter, as long as the double disk openers have the strength and sharpness to cut through soil and crop residue. If coulters are mounted on the planter unit instead of on the planter frame, it is important to pay attention to sufficient spring-pressure on the planter unit to enable both coulter and double-disk openers to be pressed into the soil.

Figure 3. Extra coulters means extra weight needed on zone-till planters for adequate penetration.

Drills need to be properly set up to allow penetration as well. This is important when you plant soybeans.

Finally, assure that you have enough weight on the planter or drill. In dry soil conditions you need at least 500 lbs per row. This means that a 6-row corn planter needs to weigh at least 3,000 lbs. You can add at least 250 lbs needed for each extra coulter. This can become an issue when using the Rawson Zone-Till system. With two extra coulters per row you need also 500 lbs of extra weight, or basically double the weight of the planter. If you have insufficient weight on the planter, it is possible to lift the whole planter up to the point where the wheel that drives the metering system doesn’t have soil contact. Weight is of course very critical when we talk about drills. A 10-foot drill with units at 7.5″ spacing has 16 units to press into the soil. The drill needs to weigh 8,000 lbs to do an adequate job, especially for soybean planting.

Sjoerd Duiker, swd10@psu.edu
Soil Management, Crop and Soil Sciences

EXPENSIVE NITROGEN

With the high price of nitrogen fertilizer we are experiencing, the big question is how should we manage N this year? Unfortunately, as long as energy prices are high N prices will be high. Corn needs N and it would be false economy to not apply N just because it is expensive. However there are some things that we can do to get the most out of the N we apply. First, account for all sources of N including:

The Penn State Agronomy Guide in Chapter 2 provides guidance and tables to help you decide how much is already there for the crop from these sources.

Especially on fields with a manure history, consider delaying all or the bulk of your N application until sidedressing time and then use the Pre-sidedress Soil Nitrate Test (PSNT) or Chlorophyll Meter Test to assess the nitrogen supply in the soil and come up with a better N recommendation. You do not need to test all fields but testing a few representative field can be very beneficial. Delaying application not only allows you to use these tests and come up with a better recommendation, but you will also have a better idea of the potential of the crop in June than you have right now (Will the drought continue???) and just by delaying application of your N, you will get consistently better nitrogen use efficiency by the crop than you will applying all of your N before planting. At high N prices the economic optimum N rate is less than at lower prices so there is justification for reducing N rates slightly, however even if you don’t cut back, at least don’t apply more than is recommended. Finally, remember that urea, UAN solution N, and manure are all subject to significant volatilization losses which can be over 30% of the N. If you are in a conventional or reduced tillage system try to get the manure or fertilizer incorporated as soon as practical after application. In no-till try to apply just before a soaking rain or consider dribbling the N in a band rather than spraying it over the whole surface. Dribbling gives you about 75% of the benefit from incorporation with little or no additional cost.

Also, urease inhibitors, like Agrotain®, are very effective at reducing N volatilization from urea containing materials if the urea cannot be immediately incorporated. This provides and extra 10–14 day to get rain or tillage to incorporate the N. There is not much we can do to change the price of N, but we can do something about the value we get from the N we buy. Efficient use of N has always been important, but now more than ever.

Douglas Beegle, dbb@psu.edu
Soil Fertility and Nutrient Management, Crop and Soil Sciences

Pest Management

WHEAT AND BARLEY DISEASE UPDATE

Wheat and barley in many parts state has survived the winter well, and stands appear to be strong in most fields. Barley is approaching flag leaf emergence in the SE portions of state and wheat will not be fair behind. In the central portions of the state, the wheat is now jointing in many fields.

I have two updates for you regarding disease management.

Issue 1: As you may recall, I discovered leaf rust in wheat and barley late last fall and suggested we check fields again this spring to see if the rust overwintered locally. Based on my observations here in Centre Co. and Lancaster, Co., it appears that leaf rust has indeed over wintered in both wheat and barley this year. I suggest that you check fields in your area to confirm the presence of rust. Symptoms of the disease include tiny orange or red colored lesions of the lower leaves. The lesion may be surrounded by a thin yellow halo on many varieties. fields found to have leaf rust should be monitored for disease development. I suspect that most fields will not need a fungicide application, however, if leaf rust can be found on the flag leaves at heading, a fungicide application may be needed to protect the plants during grain fill.

Issue 2: The label for Tilt fungicide was changed this year to allow for slightly later applications of this product. The product can now be applied to wheat at full head emergence (growth stage 10.5). This extension of the application timing also means that we may see some suppression of head scab if Tilt is applied at G.S.10.5. Please note that the label has not changed for other small grains and only permits application until the ligule (colar) of the flag leaf is visible for barley, rye, oats and triticale.

Erick DeWolf, edd10@psu.edu
Plant Pathology

DROUGHT, WEEDS, AND HERBICIDES

Well, it’s corn planting time and the forecast is looking dry. Because of the potential for dry conditions during the growing season, it is necessary to conserve as much soil moisture as possible for the crop to use. One way to help is by controlling weeds with an effective burndown program prior to planting. The only things the weeds are doing right now is using valuable moisture and making themselves larger and more difficult to control in the process. Droughty conditions can also cause problems for burndown herbicides as well. (Refer to Bill Curran’s article in the previous issue of Field Crop News (Vol. 06:01) for some general rules to consider when using burndown herbicides.) Dry weather can affect both soil applied and postemergence herbicide performance. What generally happens is there is not enough rainfall to activate the herbicide, but just enough moisture to cause weeds to germinate, emerge, and not be affected by the herbicide; thus giving them the advantage. All soil applied herbicides require rainfall to mobilize them for effective weed control. In general, rainfall should occur within 7 to 10 days after application or before weed emergence. As a general rule of thumb, ½ inch of rain is considered the minimum depending on current soil moisture levels and the herbicide used. The less mobile materials (Prowl, Atrazine, Scepter) and deeper germinating weeds (e.g. yellow nutsedge, cocklebur, velvetleaf, ragweed, etc.) will require more rainfall for effective mobilization. If 10 days have past without rainfall following a Pre treatment and weeds are starting to break, start planning for a post herbicide application, or think about using that old cultivator that you have been dying to try again. Although some "reach back" can be expected on small annual weeds (esp. broadleaves) with some herbicides when rainfall occurs, depending on this may be a little like gambling in Las Vegas. In particular, the newer pigment inhibiting herbicides (Balance Pro, Lumax, Lexar) tend to have better “reach back” potential then some other herbicides and escaped grass control is probably of greater concern. As for post herbicide applications, remember that small annual weeds are easier to kill than large ones and examine adjuvant options to maximize activity under dry weather conditions. Delaying the herbicide application until after a rainfall rarely increases your chances of success unless you're making that decision while watching a large storm front move in from the west.

Dwight Lingenfelter, dxl18@psu.edu
Weed Management, Crop and Soil Sciences